Upcoming RD platforms have deviations in various definitions of
platform macros from that of the exisiting platforms. In preparation
for adding support for those upcoming RD platforms, refactor the
header file inclusion to allow newer platforms to use a different
set of platform macros.

Change-Id: Ic80283ddadafaa7f766f300652cb0d4e507efdb6
Signed-off-by: Aditya Angadi <aditya.angadi@arm.com>