ANDROID: mm: add reclaim_shmem_address_space() for faster reclaims

Add the functionality that allow users of shmem to reclaim its pages
without going through the kswapd/direct reclaim path. An example usecase
is: Say that device allocates a larger amount of shmem pages and shares
it with hardware. To faster reclaims such pages, drivers can register
the shrinkers and call reclaim_shmem_address_space().

The implementation of this function is mostly borrowed from
reclaim_address_space() implemented for per process reclaim[1].

[1] https://lore.kernel.org/patchwork/cover/378056/



Bug: 187798288
Change-Id: I03d2c3b9610612af977f89ddeabb63b8e9e50918
Signed-off-by: Charan Teja Reddy <charante@codeaurora.org>