drm/i915: Use kmap_local_page() in gem/i915_gem_shmem.c

The use of kmap_atomic() is being deprecated in favor of
kmap_local_page()[1].

The main difference between atomic and local mappings is that local
mappings doesn't disable page faults or preemption (the preemption is
disabled for !PREEMPT_RT case, otherwise it only disables migration).

With kmap_local_page(), we can avoid the often unwanted side effect of
unnecessary page faults or preemption disables.

In drm/i915/gem/i915_gem_shmem.c, the function shmem_pwrite() need to
disable pagefault to eliminate the potential recursion fault[2]. But
here __copy_from_user_inatomic() doesn't need to disable preemption and
local mapping is valid for sched in/out.

So it can use kmap_local_page() / kunmap_local() with
pagefault_disable() / pagefault_enable() to replace atomic mapping.

[1]: https://lore.kernel.org/all/[email protected]
[2]: https://patchwork.freedesktop.org/patch/295840/

Suggested-by: Ira Weiny <[email protected]>
Suggested-by: Fabio M. De Francesco <[email protected]>
Signed-off-by: Zhao Liu <[email protected]>
Reviewed-by: Ira Weiny <[email protected]>
Reviewed-by: Fabio M. De Francesco <[email protected]>
Signed-off-by: Tvrtko Ursulin <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]

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