drm/i915: Program GMBUS Frequency based on the CDCLK for VLV.

drm/i915: Program GMBUS Frequency based on the CDCLK for VLV.

CDCLK is used to generate the gmbus clock.  This is normally done by
BIOS. Program the value if the BIOS-less system doesn't do it.

v2: Move this to intel_i2c_reset to allow reprogram the gmbus frequency
during resume. (Daniel)

v3: Change GMBUS_FREQ to GMBUSFREQ_VLV, and use VLV_DISPLAY_BASE.
(Ville).
	Remove cdclk_ratio[] table, and calculate the cdclk ratio instead.
(Ville).
 	Change the shift then mask for reg read, to mask first, then shift.
(Ville).
	Remove the gmbus frequency calculation = cdclk/1.01.  Based on BIOS
programming, gmbus frequency = cdclk frequency. (Ville)
	Add get_disp_clk_div, which can use to get cdclk/czclk divide.

v4: Fix the mmio_offset base for CZCLK_CDCLK_FREQ_RATIO, gmbus_freq
calculation, and duplicate check for gmbus_freq. (Ville)

In VLV, the spec is wrong about 4Mhz reference frequency for GMBUS. It
should be 1Mhz.

Signed-off-by: Chon Ming Lee <chon.ming.lee@intel.com>
[danvet: Add the comment Ville suggested. Also appease checkpatch a
bit.]
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>