GKI: mali_kbase: port driver to android-gs-pixel-mainline

* Convert references of mmap_sem to mmap_lock
* Update call to get_user_pages_remote() for linux version >= 5.8

Bug: 166155449
Test: booted slider with ACK-staging, verify gpu device probes
Signed-off-by: Will McVicker <willmcvicker@google.com>
Change-Id: I56be14c3716a2a4bbd6a7a650a8ed0e6560d2b36