drm: remove legacy drm_pci_alloc/free abstraction

The drm_pci_alloc/free abstraction of the dma-api is no longer required,
remove it.

Signed-off-by: Joseph Kogut <joseph.kogut@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20210423020248.3427369-2-joseph.kogut@gmail.com