drm/i915: Use _MMIO_PIPE() for SKL_BOTTOM_COLOR

No need to use _MMIO_PIPE2() for SKL_BOTTOM_COLOR
since all pipe registers are evenly spread on skl+.
Switch to _MMIO_PIPE() and thus avoid the hidden dev_priv.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221026113906.10551-3-ville.syrjala@linux.intel.com


Reviewed-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>