drm/radeon: implement pci config reset for evergreen/cayman (v2)

pci config reset is a low level reset that resets
the entire chip from the bus interface.  It can
be more reliable if soft reset fails.

v2: put behind module parameter

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

diff --cc drivers/gpu/drm/radeon/evergreen.c
Simple merge

diff --cc drivers/gpu/drm/radeon/evergreend.h
Simple merge

diff --cc drivers/gpu/drm/radeon/ni.c
Simple merge