getProcessFreezeInfo reads more info from kernel

Improve primitive binder function to check if a process has any pending
binder transactions so that the freezer policy can choose to wait and
drain those pending transactions.

Bug: 198493121
Test: app launch/foreground/background stress test
Change-Id: Ia7ce6899ddaeb8e8453b0b8f3536d129b6b761d3