drm/i915: Use huge tmpfs mountpoint helpers

drm/i915: Use huge tmpfs mountpoint helpers

Make use of the new drm_gem_huge_mnt_create() and
drm_gem_get_huge_mnt() helpers to avoid code duplication. Now that
it's just a few lines long, the single function in i915_gemfs.c is
moved into i915_gem_shmem.c.

v3:
- use huge tmpfs mountpoint in drm_device
- move i915_gemfs.c into i915_gem_shmem.c

v4:
- clean up mountpoint creation error handling

v5:
- use drm_gem_has_huge_mnt() helper

v7:
- include <drm/drm_print.h> in i915_gem_shmem.c

v8:
- keep logging notice message with CONFIG_TRANSPARENT_HUGEPAGE=n
- don't access huge_mnt field with CONFIG_TRANSPARENT_HUGEPAGE=n

v9:
- replace drm_gem_has_huge_mnt() by drm_gem_get_huge_mnt()
- remove useless ternary op test in selftests/huge_pages.c

v12:
- fix layering violation in selftests (Tvrtko)
- fix incorrect filename in commit message

v13:
- add Tvrtko A-b

Signed-off-by: Loïc Molinari <loic.molinari@collabora.com>
Acked-by: Tvrtko Ursulin <tursulin@ursulin.net>
Link: https://patch.msgid.link/20251205182231.194072-6-loic.molinari@collabora.com
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>