drm/i915/backlight: drop DISPLAY_MMIO_BASE() use from backlight registers

None of the remaining backlight registers that use DISPLAY_MMIO_BASE()
are used on VLV/CHV, which are the only platforms that have non-zero
base. Just drop the DISPLAY_MMIO_BASE() use, reducing the implicit
dev_priv references.

Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/75ae3f2945912f908df2444d4f0ab97a23b89897.1670405587.git.jani.nikula@intel.com

drm/i915/backlight: use VLV_DISPLAY_BASE for VLV/CHV backlight registers

Since the VLV/CHV backlight registers are only used on VLV/CHV, there's
no need to dynamically look up DISPLAY_MMIO_BASE(). We know it's
VLV_DISPLAY_BASE. Use it statically, reducing the implicit dev_priv
references.

Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/eb252083a56ec64b4fdb58d4d30abcf305a3a9c2.1670405587.git.jani.nikula@intel.com

drm/i915: split out intel_display_reg_defs.h

Split out the display register helper macros to a separate file. For
now, include it from i915_reg.h, but note that there are already files
that don't need i915_reg.h, such as intel_audio.c.

Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/3af47193ff5219b6d2cfe353b752ec4bb44de4f1.1668008071.git.jani.nikula@intel.com

drm/i915/backlight: split out backlight registers to a separate file

Declutter i915_reg.h by splitting backlight registers to a separate
file. Also include the utility pin definitions, even though they are
used for non-backlight things too.

Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Arun R Murthy <arun.r.murthy@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220815094838.3511723-1-jani.nikula@intel.com