CMake: Create CMSIS library targets to remove dependency on MBED_TARGET_LABELS ...

This goes towards eventually removing reliance on targets.json to specify
the requirements of Mbed targets.

CMake: Refactor Freescale targets ...

Refactor all Freescale targets to be CMake buildsystem targets. This removes
the need for checking MBED_TARGET_LABELS repeatedly and allows us to be
more flexible in the way we include MBED_TARGET source in the build.

A side effect of this is it will allow us to support custom targets
without breaking the build for 'standard' targets, as we use CMake's
standard mechanism for adding build rules to the build system, rather
than implementing our own layer of logic to exclude files not needed for
the target being built. Using this approach, if an MBED_TARGET is not
linked to using `target_link_libraries` its source files will not be
added to the build. This means custom target source can be added to the
user's application CMakeLists.txt without polluting the build system
when trying to compile for a standard MBED_TARGET.

CMake: Add support for Freescale KLXX targets ...

All Freescale KLXX targets supported by Mbed OS
can now be built with CMake.

CMake: Use relative paths to list source files and directories ...

The absolute path is still required for listing linker
files as they are referenced from a function in the top
level CMake input source file.

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: replace usage of the mbed_add_cmake_directory_if_labels() function (#13754) ...

Directories that start with special prefixes (TARGET_, FEATURE_, COMPONENT_)  are added to the build based on Mbed target configuration from targets.json instead of calling utility function mbed_add_cmake_directory_if_labels().

CMake: Fix failure due to events and netsocket dirs changes

CMake: Add support for K64F target