DRM: remove drm_pci_device_is_pcie

drm_pci_device_is_pcie duplicates the funcationality of pci_is_pcie.
Convert callers of the former to the latter.  This has the side benefit
of removing an unnecessary search in the PCI configuration space due to
using a saved PCIe capability offset.

[airlied: update for new callsite]

Signed-off-by: Jon Mason <jdmason@kudzu.us>
Signed-off-by: Dave Airlie <airlied@redhat.com>