PDK: Disable libRS for PDK builds

libRS is breaking PDK builds, because it depends on projects not available in
the PDK.

Bug: 62086238
Test: Validated PDK builds are no longer broken due to libRS
Change-Id: I17cc403fa90b9a0ca4d10c96e3469d3b66ae4275
diff --git a/Android.bp b/Android.bp
index 4d05b23..5ea81fb 100644
--- a/Android.bp
+++ b/Android.bp
@@ -54,6 +54,12 @@
 
         "libbcinfo",
     ],
+
+    product_variables: {
+        pdk: {
+            enabled: false,
+        },
+    },
 }
 
 // Build rsg-generator ====================
@@ -202,6 +208,9 @@
         override_rs_driver: {
             cflags: ["-DOVERRIDE_RS_DRIVER=%s"],
         },
+        pdk: {
+            enabled: false,
+        },
     },
 }
 
@@ -234,6 +243,12 @@
         "libandroid_runtime",
     ],
 
+    product_variables: {
+        pdk: {
+            enabled: false,
+        },
+    },
+
     static_libs: ["libRSDispatch"],
 
     version_script: "libRS.map",