Add TARGET_CPU_VARIANT := cortex-a15 for Manta.

-mcpu=cortex-a15 will be derived from it and passed to GCC.

Bug: 7961327.
Change-Id: Ia5e939c9308745914aa3a47ae150097294b3929b
diff --git a/BoardConfig.mk b/BoardConfig.mk
index 811bdf6..0df8bfd 100755
--- a/BoardConfig.mk
+++ b/BoardConfig.mk
@@ -30,6 +30,7 @@
 TARGET_CPU_SMP := true
 TARGET_ARCH := arm
 TARGET_ARCH_VARIANT := armv7-a-neon
+TARGET_CPU_VARIANT := cortex-a15
 ARCH_ARM_HAVE_TLS_REGISTER := true
 
 #Bluetooth