drm/i915/crt: Clean up ADPA_HOTPLUG_BITS definitions

drm/i915/crt: Clean up ADPA_HOTPLUG_BITS definitions

ADPA_HOTPLUG_BITS is defined in terms of the individual
register bits and is defined in intel_crt.c, whereas the
counterpart mask (ADPA_CRT_HOTPLUG_MASK) is just defined
as a raw hex constant and lives in i915_reg.h. Just define
both the same way (with unified name to boot) and move both
to intel_crt.c since they are more an implementation detail
rather than anything to do with the actual register definitions.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241107161123.16269-6-ville.syrjala@linux.intel.com
Reviewed-by: Jani Nikula <jani.nikula@intel.com>