Add vendor-ramdisk image to Soong.

Add vendor_ramdisk_available and vendor_ramdisk attribute to
various rules. When a vendor_ramdisk variant of a module is
generated, it is installed to $OUT/vendor-ramdisk.

It is similar to a ramdisk image.
Test: m nothing -j

Change-Id: Ib2d16459f3094dbe21c3bdb7c016cb4b2bf62765

android/arch.go

@@ -914,8 +914,8 @@ func archMutator(bpctx blueprint.BottomUpMutatorContext) {
 		osTargets = targets
 	}
 
-	// only the primary arch in the ramdisk / recovery partition
-	if os == Android && (module.InstallInRecovery() || module.InstallInRamdisk()) {
+	// only the primary arch in the ramdisk / vendor_ramdisk / recovery partition
+	if os == Android && (module.InstallInRecovery() || module.InstallInRamdisk() || module.InstallInVendorRamdisk()) {
 		osTargets = []Target{osTargets[0]}
 	}