Make mainline device use armv8-a

Change Iede5830093497abe753a34df3bc4913468be39d0 changed
the arch variant to armv8-2a uncondtionally, but for
mainline we want armv8-a.

Test: make
Change-Id: I31e7cbd9a879cdf857ac03684919d6fecb5f15c7

BoardConfig-common.mk

diff --git a/BoardConfig-common.mk b/BoardConfig-common.mk
index 386ebe1..8beed4f 100644
--- a/BoardConfig-common.mk
+++ b/BoardConfig-common.mk
@@ -34,7 +34,11 @@
 endif
 
 TARGET_2ND_ARCH := arm
+ifeq (,$(filter %_mainline,$(TARGET_PRODUCT)))
 TARGET_2ND_ARCH_VARIANT := armv8-2a
+else
+TARGET_2ND_ARCH_VARIANT := armv8-a
+endif
 TARGET_2ND_CPU_ABI := armeabi-v7a
 TARGET_2ND_CPU_ABI2 := armeabi
 ifeq (,$(filter %_mainline,$(TARGET_PRODUCT)))