Use -mcpu=cortex-a15 for gcc arch dependent compilation.

If TARGET_CPU_VARIANT=cortex-a15 is specified in the BoardConfig.mk file.

Bug: 7961327
Change-Id: Ic459df378293237c54263f5315ac3be62dad4273

core/combo/arch/arm/armv7-a-neon.mk

@@ -13,11 +13,13 @@ ARCH_ARM_HAVE_VFP               := true
 ARCH_ARM_HAVE_VFP_D32           := true
 ARCH_ARM_HAVE_NEON              := true
 
-# Note: Hard coding the 'tune' value here is probably not ideal,
-# and a better solution should be found in the future.
-#
-arch_variant_cflags := \
-    -march=armv7-a \
+ifeq ($(strip $(TARGET_CPU_VARIANT)), cortex-a15)
+	arch_variant_cflags := -mcpu=cortex-a15
+else
+	arch_variant_cflags := -march=armv7-a
+endif
+
+arch_variant_cflags += \
     -mfloat-abi=softfp \
     -mfpu=neon