[vulkan] Add feature flag

bug: 111137294

This allows us to build the HAL, but not activate it unless a
feature flag is enabled.

If the feature flag is not enabled, the stub hal is used.

Change-Id: I678a1eea0f36fd1574c78a400676f7189a8fc53c
diff --git a/system/vulkan_enc/ResourceTracker.cpp b/system/vulkan_enc/ResourceTracker.cpp
index a693ebd..3cacf39 100644
--- a/system/vulkan_enc/ResourceTracker.cpp
+++ b/system/vulkan_enc/ResourceTracker.cpp
@@ -328,6 +328,12 @@
         }
     }
 
+    bool hostSupportsVulkan() const {
+        if (!mFeatureInfo) return false;
+
+        return mFeatureInfo->hasVulkan;
+    }
+
     bool usingDirectMapping() const {
         return mHostVisibleMemoryVirtInfo.virtualizationSupported;
     }
@@ -1136,6 +1142,10 @@
     mImpl->setupFeatures(features);
 }
 
+bool ResourceTracker::hostSupportsVulkan() const {
+    return mImpl->hostSupportsVulkan();
+}
+
 bool ResourceTracker::usingDirectMapping() const {
     return mImpl->usingDirectMapping();
 }