drm/i915/aux: add separate register macros and functions for VLV/CHV

Add separate macros for VLV/CHV registers without the implicit dev_priv,
and with the display MMIO base baked in.

A number of implicitly used dev_priv local variables can be removed.

Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Nirmoy Das <nirmoy.das@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231011201533.1081368-1-jani.nikula@intel.com