gralloc: Set min_sdk_version

Modules contributing mainline modules (APK/APEX) should set
min_sdk_version.

For now setting min_sdk_version doesn't change build outputs.
But build-time checks will be added soon.

Bug: 152655956
Test: m
Change-Id: I06644a725eb8f4ce0c7d8e1f09359b55e1b668d7

libgrallocusage/Android.bp

@@ -26,4 +26,5 @@ cc_library {
     export_include_dirs: ["include"],
     shared_libs: ["android.hardware.graphics.allocator@2.0"],
     header_libs: ["libhardware_headers"],
+    min_sdk_version: "29",
 }