feat(sgi): remove unused SGI_PLAT build-option

Currently, the common makefile has reference to "SGI_PLAT" build-option.
This however is not set by any of the platforms that makes use of the
common makefile. Therefore, remove the unused SGI_PLAT build-option.

Signed-off-by: Rohit Mathew <Rohit.Mathew@arm.com>
Change-Id: I6cc0b8d87222c7b3aef998774cee964a920cceb6
1 file changed