PL2: Set TARGET_2ND_ARCH_VARIANT as armv8-a

Change from armv7-a-neon to armv8-a for 32-bit shared
libraries ABI compatibility.

CRs-Fixed: 2262190

Change-Id: I160bb25fb84b13bdb7604e46df534c0d60bfedae

BoardConfig.mk

@@ -34,7 +34,7 @@ TARGET_CPU_ABI2 :=
 TARGET_CPU_VARIANT := generic
 
 TARGET_2ND_ARCH := arm
-TARGET_2ND_ARCH_VARIANT := armv7-a-neon
+TARGET_2ND_ARCH_VARIANT := armv8-a
 TARGET_2ND_CPU_ABI := armeabi-v7a
 TARGET_2ND_CPU_ABI2 := armeabi
 TARGET_2ND_CPU_VARIANT := cortex-a53