Set apex_available property

The marked library(ies) were available to the APEXes via the
hand-written whitelist in build/soong/apex/apex.go. Trying to remove the
whitelist by adding apex_available property to the Android.bp of the
libraries.

Bug: 150999716
Test: m
Change-Id: Id08058f3105463558c6c82298344a33af0efb2d3

libprocessgroup/Android.bp

@@ -13,6 +13,10 @@ cc_library_headers {
             enabled: true,
         },
     },
+    apex_available: [
+        "//apex_available:platform",
+        "//apex_available:anyapex",
+    ],
 }
 
 cc_library {
@@ -52,4 +56,8 @@ cc_library {
         "-Werror",
         "-Wexit-time-destructors",
     ],
+    apex_available: [
+        "//apex_available:platform",
+        "//apex_available:anyapex",
+    ],
 }