refactor(plat/sgi): header files and macros

In preparation to add support for the latest Neoverse reference design
platforms, reorganize the header files to allow newer platforms to use a
different set of platform macros. In addition to this, rename the macros
to match the names used in trusted firmware.

Signed-off-by: Shriram K <shriram.k@arm.com>
Change-Id: Ic21601730650d59ed8e40f763a0d5c4a5c45d3a3
11 files changed