processgroup: Set min_sdk_version

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

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: Idaa27ce24cc13d13145eaef85a08b9033922c7bc

libprocessgroup/Android.bp

@@ -17,6 +17,7 @@ cc_library_headers {
         "//apex_available:platform",
         "//apex_available:anyapex",
     ],
+    min_sdk_version: "29",
 }
 
 cc_library {
@@ -60,4 +61,5 @@ cc_library {
         "//apex_available:platform",
         "//apex_available:anyapex",
     ],
+    min_sdk_version: "29",
 }