ANDROID: vendor_hooks: add hook for shmem memory stat

Add some vendor hooks for shmem memory stats. This help us track the
number of shmem pages which are belong to the mapping we're interested
in. If shmem pages are swapped out, we can track that number, too.

Bug: 372282099

Change-Id: I0a18a690f37719400faa4a01b1d5d09e979f09c7
Signed-off-by: Jaewon Kim <jaewon31.kim@samsung.com>