Sanitise includes across codebase ...

Enforce full include path for includes. Deprecate old paths.

The following folders inside include/lib have been left unchanged:

- include/lib/cpus/${ARCH}
- include/lib/el3_runtime/${ARCH}

The reason for this change is that having a global namespace for
includes isn't a good idea. It defeats one of the advantages of having
folders and it introduces problems that are sometimes subtle (because
you may not know the header you are actually including if there are two
of them).

For example, this patch had to be created because two headers were
called the same way: e0ea0928d5b7 ("Fix gpio includes of mt8173 platform
to avoid collision."). More recently, this patch has had similar
problems: 46f9b2c3a282 ("drivers: add tzc380 support").

This problem was introduced in commit 4ecca33988b9 ("Move include and
source files to logical locations"). At that time, there weren't too
many headers so it wasn't a real issue. However, time has shown that
this creates problems.

Platforms that want to preserve the way they include headers may add the
removed paths to PLAT_INCLUDES, but this is discouraged.

Change-Id: I39dc53ed98f9e297a5966e723d1936d6ccf2fc8f
Signed-off-by: Antonio Nino Diaz <antonio.ninodiaz@arm.com>

Introduce object pool allocator ...

The object pool allocator provides a simplistic interface to manage
allocation in a fixed-size static array. The caller creates a static
"object pool" out of such an array and may then call pool_alloc() to
get the next available object within the pool. There is also a variant
to get multiple consecutive objects: pool_alloc_n().

Note that this interface does not provide any way to free the objects
afterwards. This is by design and it is not a limitation. We do not
want to introduce complexity induced by memory freeing, such as
use-after-free bugs, memory fragmentation and so on.

Change-Id: Iefc2e153767851fbde5841a295f92ae48adda71f
Signed-off-by: Sandrine Bailleux <sandrine.bailleux@arm.com>