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/image.go

@@ -26,6 +26,10 @@ type ImageInterface interface {
 	// ramdisk partition).
 	RamdiskVariantNeeded(ctx BaseModuleContext) bool
 
+	// VendorRamdiskVariantNeeded should return true if the module needs a vendor ramdisk variant (installed on the
+	// vendor ramdisk partition).
+	VendorRamdiskVariantNeeded(ctx BaseModuleContext) bool
+
 	// RecoveryVariantNeeded should return true if the module needs a recovery variant (installed on the
 	// recovery partition).
 	RecoveryVariantNeeded(ctx BaseModuleContext) bool
@@ -53,6 +57,9 @@ const (
 
 	// RamdiskVariation means a module to be installed to ramdisk image.
 	RamdiskVariation string = "ramdisk"
+
+	// VendorRamdiskVariation means a module to be installed to vendor ramdisk image.
+	VendorRamdiskVariation string = "vendor_ramdisk"
 )
 
 // imageMutator creates variants for modules that implement the ImageInterface that
@@ -73,6 +80,9 @@ func imageMutator(ctx BottomUpMutatorContext) {
 		if m.RamdiskVariantNeeded(ctx) {
 			variations = append(variations, RamdiskVariation)
 		}
+		if m.VendorRamdiskVariantNeeded(ctx) {
+			variations = append(variations, VendorRamdiskVariation)
+		}
 		if m.RecoveryVariantNeeded(ctx) {
 			variations = append(variations, RecoveryVariation)
 		}