ANDROID: mm: fix use-after free of page_ext in page_pinner

Apply new page_ext refcounting scheme to page_pinner.

Bug: 236222283
Bug: 240196534
[surenb: extracted from aosp/2369529]
Change-Id: I3b64caf5a7e8ff316507cc3933f5b3696142268d
Signed-off-by: Charan Teja Kalla <quic_charante@quicinc.com>
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
(cherry picked from commit 231a4ccc)
Signed-off-by: Georgi Djakov <quic_c_gdjako@quicinc.com>