Normalize the 2nd CPU architect of 64 bits arm GSI

In order to let GSI more generic. Normalize the 64 bits arm GSI
to be:

    TARGET_2ND_ARCH_VARIANT := armv8-a
    TARGET_2ND_CPU_VARIANT := generic

Bug: 64775084
Test: Build pass and boot to home screen
Change-Id: I1dd5aa8524c1d243f832372bf7e3e64fae09e945
diff --git a/target/board/generic_arm64_a/BoardConfig.mk b/target/board/generic_arm64_a/BoardConfig.mk
index 4729744..34a8ac0 100644
--- a/target/board/generic_arm64_a/BoardConfig.mk
+++ b/target/board/generic_arm64_a/BoardConfig.mk
@@ -23,7 +23,7 @@
 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 := generic
diff --git a/target/board/generic_arm64_ab/BoardConfig.mk b/target/board/generic_arm64_ab/BoardConfig.mk
index 1cab844..ea5cc96 100644
--- a/target/board/generic_arm64_ab/BoardConfig.mk
+++ b/target/board/generic_arm64_ab/BoardConfig.mk
@@ -23,11 +23,10 @@
 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
-# TODO(jiyong) can we set krait here?
-TARGET_2ND_CPU_VARIANT := cortex-a15
+TARGET_2ND_CPU_VARIANT := generic
 
 # Enable A/B update
 TARGET_NO_RECOVERY := true