Clean up top-level build file and build options, fix build issues on MinGW

drivers: Add missing OSPI.cpp to CMakeLists.txt

CMake: greentea: Port mbed-drivers-ticker to CTest ...

Call add_test in mbed_greentea_add_test and specify mbedhtrun as the
command to run.

An MBED_HTRUN_ARGUMENTS variable has been added, which is a semicolon
separated list of arguments to forward to htrun. The user is required to
pass in any arguments mbedhtrun needs to communicate with the device
under test at CMake configuration time.

We automate passing some of the htrun arguments in CMake using data
provided by mbed_config.cmake or gathered from the CMake environment.
The following arguments are passed to htrun from CMake:

* -f/--image-path
* -e/--enum-host-tests
* -m/--micro
* -R/--reset-timeout

--baud-rate is also passed if the MBED_CONF_PLATFORM_STDIO_BAUD_RATE
config parameter is defined.

Temporary checks have been added to mbed_greentea_add_test to keep the
old flow working until we port all of the greentea tests to CTest. These
checks should be removed after we make all greentea tests runnable by
CTest.

CMake: Add option to enable greentea tests ...

Add an option to enable the greentea tests independently from the unit
tests.

We can't just use the typical BUILD_TESTING option to enable greentea
tests. BUILD_TESTING enables unit tests and fetches googletest, which
are compiled for the host. Greentea tests are cross compiled and require
a toolchain file. For this reason we add a new option just to enable
greentea tests, preventing build failures triggered by the unit tests
and googletest.

CMake: Only build unit tests if Mbed OS is the current project ...

Typically when adding a unit test directory to a CMake project a check
will be used to ensure the subdirectory is added only if the following
are true:

* The BUILD_TESTING option is set to ON.
* The current CMake project is the top-level project.

The reason being, if a downstream project includes our project they
generally don't want to build our unit tests.

In mbed-os, we do correctly specify the above condition before adding
the central UNITTEST subdirectory, which fetches googletest and adds the
"stub" libraries the unit tests depend on. However, we only check if
CMAKE_CROSSCOMPILING is OFF (or undefined) before actually adding the
unit tests. This mismatched logic would lead to unexpected build
failures in various scenarios. One likely case could be: a downstream
project including mbed-os happens to set CMAKE_CROSSCOMPILING to
OFF/undefined for any reason (possibly to build its own unit tests).
mbed-os would go ahead and attempt to build its tests without fetching
googletest or adding the required stub targets.

To fix the issue replace the check for CMAKE_CROSSCOMPILING in the unit
tests with the same BUILD_TESTING idiom we use for adding the central
UNITTESTS subdirectory.

CMake: Add add_subdirectory of unittests ...

- add every libraries unittest directory into respective CMake
  which allows to include unittest source into build based on
  MBED_BUILD_UNITTESTS flag

CMake: add mbed-os and mbed-baremetal targets ...

mbed-os consists of mbed-core and mbed-rtos
mbed-baremetal consists of mbed-core

The main change is for mbed-core. Changing from object library to be interface. This way it allows us to do the above to have 2 main targets for users to use.

This should be backward compatible change as mbed-os target we used contains the same files/options as previously set.

CMake: Rename CMake targets ...

* mbed-os renamed mbed-core
* mbed-os-<COMPONENT> renamed mbed-<COMPONENT>

CMake: Componentize Mbed OS into multiple CMake targets (#13732) ...

Aside from the core mbed-os CMake target, a number of targets have been created so they can optionally be included by application executables that require them using `target_link_libraries()`.

Co-authored-by: Martin Kojtal <martin.kojtal@arm.com>
Co-authored-by: Rajkumar Kanagaraj <rajkumar.kanagaraj@arm.com>

CMake: Fix failures due to device_key and storage dirs move

CMake: Fix build failure due to drivers and lwipstack dirs move

CMake: Add support for drivers dir