Add the device config GenerateAidlNdkPlatformBackend

The config is used to force the generation of the AIDL ndk_platform
backend which will eventually be removed in favor of the ndk backend.
The switch is needed as an escape hatch for some devices whose BSP
(outsourced and thus hardly modifiable) depends on the ndk_backend
libraries.

Bug: 161456198
Test: m
Change-Id: Ie11ca62be05754bb2593da16e1380103c670b393

android/variable.go

@@ -417,6 +417,8 @@ type productVariables struct {
 
 	SepolicyFreezeTestExtraDirs         []string `json:",omitempty"`
 	SepolicyFreezeTestExtraPrebuiltDirs []string `json:",omitempty"`
+
+	GenerateAidlNdkPlatformBackend bool `json:",omitempty"`
 }
 
 func boolPtr(v bool) *bool {