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
diff --git a/plat/arm/sgi/common/plat_setup.c b/plat/arm/sgi/common/plat_setup.c
index 4b15f1a..f343f8d 100644
--- a/plat/arm/sgi/common/plat_setup.c
+++ b/plat/arm/sgi/common/plat_setup.c
@@ -24,5 +24,5 @@
 
 void plat_arm_gic_init(void)
 {
-	arm_gic_init(SGI_GICC_BASE, SGI_GICD_BASE, SGI_GICR_BASE);
+	arm_gic_init(PLAT_ARM_GICC_BASE, PLAT_ARM_GICD_BASE, PLAT_ARM_GICR_BASE);
 }