Revert "drm/vgem: Implement mmap as GEM object function"

Revert "drm/vgem: Implement mmap as GEM object function"

Commit 375cca1cfeb5 ("drm/vgem: Implement mmap as GEM object function")
broke several IGT tests in vgem_basic. [1] Attempts to fix the issue
have not worked out so far. [2][3] Revert the change for now.

Note that there is a patch that converts vgem to shmem helpers. [4]
Merging this change would be preferable to modifying vgem's mmap code.

v2:
	* fix spelling error in commit message (Daniel)

[1] https://intel-gfx-ci.01.org/tree/drm-tip/igt@vgem_basic@unload.html
[2] https://lore.kernel.org/intel-gfx/20210709154256.12005-1-tzimmermann@suse.de/
[3] https://lore.kernel.org/intel-gfx/20210712123321.3658-1-tzimmermann@suse.de/
[4] https://patchwork.freedesktop.org/series/90671/

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Fixes: 375cca1cfeb5 ("drm/vgem: Implement mmap as GEM object function")
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Christian König <christian.koenig@amd.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: "Christian König" <christian.koenig@amd.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Melissa Wen <melissa.srw@gmail.com>
Cc: Qinglang Miao <miaoqinglang@huawei.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210713090235.26372-1-tzimmermann@suse.de