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>

Add two new functions 'plat_arm_sgi_get_platform_id' and
'plat_arm_sgi_get_config_id' which will be implemented by all the
SGI platforms. These functions can be used to determine the part
number and configuration id of the SGI platforms.

In BL2, these functions are used to populate the 'system-id' node.
In BL31, these functions are used to populate the 'sgi_plat_info_t'
structure with the part number and configuration id of the platform.

Change-Id: I3bacda933527724a3b4074ad4ed5b53a81ea4689
Signed-off-by: Chandni Cherukuri <chandni.cherukuri@arm.com>