For reducing the splat of is_haswell_plus() or such macros, this patch
introduces pin_cvt_fixup() ops to hdmi_spec.  For HSW+ and VLV+
codecs, set this ops so that the driver can call the Intel-specific
workarounds appropriately.

A gratis bonus that we can remove the mux_id argument from
hdmi_choose_cvt(), too, since the fixup function always refers the
mux_idx from the given per_pin object.
Signed-off-by: NTakashi Iwai <tiwai@suse.de>