drm/i915: rename some HDMI bit definitions

Bits used only on HDMI mode now have HDMI_ prefix instead of SDVO_.
The COLOR_FORMAT bits now have prefixes (and the 12bpc bit is for HDMI
only).

Notice that this patch uncovers a bug on the SDVO code: the
COLOR_RANGE_16_235 bit can only be used if the port is in TMDS mode,
not SDVO mode. This will have to be fixed in a later patch.

Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>