HACK: use arm64 prebuilts from apex sets for riscv64

There are no riscv64 prebuilts in apex sets, use arm64 ones for
now.

Test: lunch aosp_riscv64-userdebug && m droid dist
Change-Id: Iee2d669e01d93504642223939857634b7fd1c1ba

java/app_set.go

@@ -92,7 +92,8 @@ func (as *AndroidAppSet) APKCertsFile() android.Path {
 var TargetCpuAbi = map[string]string{
 	"arm":   "ARMEABI_V7A",
 	"arm64": "ARM64_V8A",
-	"riscv64": "RISCV64",
+	// TODO: use "RISCV64" when that is supported in bundles
+	"riscv64": "ARM64_V8A",
 	"x86":     "X86",
 	"x86_64":  "X86_64",
 }