Add support for an armv8 variant for Kryo

* Use mcpu=cortex-a57, since it is the closest to Kryo.
* Clang doesn't support Kryo as a target yet.

Bug: 36728278

Test: Built and booted a sailfish using Kryo.

Change-Id: Ic0c9588d86fba41896e50e3f0cf0d2b310ffee93
Signed-off-by: Alex Naidis <alex.naidis@linux.com>

android/arch.go

@@ -859,6 +859,7 @@ func getMegaDeviceConfig() []archConfig {
 		{"arm", "armv7-a-neon", "kryo", []string{"armeabi-v7a"}},
 		{"arm64", "armv8-a", "cortex-a53", []string{"arm64-v8a"}},
 		{"arm64", "armv8-a", "denver64", []string{"arm64-v8a"}},
+		{"arm64", "armv8-a", "kryo", []string{"arm64-v8a"}},
 		{"mips", "mips32-fp", "", []string{"mips"}},
 		{"mips", "mips32r2-fp", "", []string{"mips"}},
 		{"mips", "mips32r2-fp-xburst", "", []string{"mips"}},