Fix PDK build

This commit disables "bootstat" in PDK builds because "bootstat" depends
on "libstatslog" (from "frameworks/base") which is not included in PDK
builds as well.

Test: Build a target (described in http://b/72961456) with
`platform.zip` built from master FSK source tree.

Bug: 72961456
Change-Id: I06b1555694510e17ea82d5c6dfcdeaf99b905e4d

bootstat/Android.bp

@@ -66,6 +66,9 @@ cc_binary {
     shared_libs: ["liblogcat"],
     init_rc: ["bootstat.rc"],
     product_variables: {
+        pdk: {
+            enabled: false,
+        },
         debuggable: {
             init_rc: ["bootstat-debug.rc"],
         },