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
diff --git a/cc/vendor_snapshot.go b/cc/vendor_snapshot.go
index 64e3ea8..78bde38 100644
--- a/cc/vendor_snapshot.go
+++ b/cc/vendor_snapshot.go
@@ -1005,9 +1005,10 @@
 		// But we can't just check SocSpecific() since we already passed the image mutator.
 		// Check ramdisk and recovery to see if we are real "vendor: true" module.
 		ramdisk_available := module.InRamdisk() && !module.OnlyInRamdisk()
+		vendor_ramdisk_available := module.InVendorRamdisk() && !module.OnlyInVendorRamdisk()
 		recovery_available := module.InRecovery() && !module.OnlyInRecovery()
 
-		if !ramdisk_available && !recovery_available {
+		if !ramdisk_available && !recovery_available && !vendor_ramdisk_available {
 			vendorSnapshotsLock.Lock()
 			defer vendorSnapshotsLock.Unlock()