drm: move pci bus master enable into driver.
The current enabling of bus mastering in the drm midlayer allows a large race condition under kexec. When a kexec'ed kernel re-enables bus mastering for the GPU, previously setup dma blocks may cause writes to random pieces of memory. On radeon the writeback mechanism can cause these sorts of issues. This patch doesn't fix the problem, but it moves the bus master enable under the individual drivers control so they can move enabling it until later in their load cycle and close the race. Fix for radeon kms driver will be in a follow-up patch. Signed-off-by: Dave Airlie <firstname.lastname@example.org>