ANDROID: mm: add get_page_owner_handle function

Add and export get_page_owner_handle function which returns
the handle for the corresponding page_ext, this will be used
by the minidump module to get page_owner info.

Bug: 394900912
Bug: 199236943
Bug: 444616776
Change-Id: I7b3641f7c6ad918f4111c98d715904477f92185b
Signed-off-by: Vijayanand Jitta <vjitta@codeaurora.org>
Signed-off-by: Jaskaran Singh <quic_jasksing@quicinc.com>
Signed-off-by: Ketan Kishore <ketan.kishore@oss.qualcomm.com>