Add missing pieces of ARMv9.2-A support.

aosp/3255916 didn't add all of the required infrastructure.
Refactor it to be more like x86_64 so it requires less
boilerplate code.

Bug: 364383722
Test: presubmit
Change-Id: Idc5279ffc5fe964bea9f98873c01468944d90091
diff --git a/android/arch_list.go b/android/arch_list.go
index 2937092..9501c87 100644
--- a/android/arch_list.go
+++ b/android/arch_list.go
@@ -26,6 +26,7 @@
 		"armv8-2a",
 		"armv8-2a-dotprod",
 		"armv9-a",
+		"armv9-2a",
 	},
 	X86: {
 		"amberlake",