drm/i915: Pass explicit mode into mode_from_pipe_config v3

We want to reuse this in the fbdev initial config code independently
from any fastboot hacks. So allow a bit more flexibility.

v2: Forgot to git add ...
v3: make non-static (Jesse)

Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

diff --cc drivers/gpu/drm/i915/intel_display.c
Simple merge

diff --cc drivers/gpu/drm/i915/intel_drv.h
Simple merge