rust: Add rust_ffi_static vendor ramdisk Support

Similar to our vendor support, this adds support for linking rust static
libraries to vendor ramdisk cc modules.

A bug fix is also included where a restriction against setting rust_ffi
vendor-specific was not being enforced.

Bug: 179397942
Test: Example modules link, Soong tests pass.
Change-Id: I737cdf0c2f49ab349bcea2a0429e6298ebc1313e
diff --git a/cc/androidmk.go b/cc/androidmk.go
index ddb81d9..8652c10 100644
--- a/cc/androidmk.go
+++ b/cc/androidmk.go
@@ -26,9 +26,9 @@
 var (
 	nativeBridgeSuffix  = ".native_bridge"
 	productSuffix       = ".product"
-	vendorSuffix        = ".vendor"
+	VendorSuffix        = ".vendor"
 	ramdiskSuffix       = ".ramdisk"
-	vendorRamdiskSuffix = ".vendor_ramdisk"
+	VendorRamdiskSuffix = ".vendor_ramdisk"
 	recoverySuffix      = ".recovery"
 	sdkSuffix           = ".sdk"
 )