drm/i915: Wean off drm_pci_alloc/drm_pci_free

drm_pci_alloc and drm_pci_free are just very thin wrappers around
dma_alloc_coherent, with a note that we should be removing them.
Furthermore since

commit de09d31d
Author: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Date:   Fri Jan 15 16:51:42 2016 -0800

    page-flags: define PG_reserved behavior on compound pages

    As far as I can see there's no users of PG_reserved on compound pages.
    Let's use PF_NO_COMPOUND here.

drm_pci_alloc has been declared broken since it mixes GFP_COMP and
SetPageReserved. Avoid this conflict by weaning ourselves off using the
abstraction and using the dma functions directly.

Reported-by: Taketo Kabe
Closes: https://gitlab.freedesktop.org/drm/intel/issues/1027
Fixes: de09d31d

 ("page-flags: define PG_reserved behavior on compound pages")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: <stable@vger.kernel.org> # v4.5+
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20200202153934.3899472-1-chris@chris-wilson.co.uk