ANDROID: page_pinner: prevent pp_buffer access before initialization

If page_pinner is configured with page_pinner_enabled=false and
failure_tracking=true, pp_buffer will be accessed without being
initialized. Prevent this by adding page_pinner_inited checks in
functions that access it.

Fixes: 898cfbf0 ("ANDROID: mm: introduce page_pinner")
Bug: 259024332
Bug: 260179017
Change-Id: I8f612cae3e74d36e8a4eee5edec25281246cbe5e
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
(cherry picked from commit 23fb3111)