drm/i915/display: Abstract pipe/trans/cursor offset calculation

drm/i915/display: Abstract pipe/trans/cursor offset calculation

Introduce INTEL_DISPLAY_DEVICE_*_OFFSET() macros to compute absolute
MMIO offsets for pipe, transcoder, and cursor registers.

Update _MMIO_PIPE2/_MMIO_TRANS2/_MMIO_CURSOR2 to use these macros
for cleaner abstraction and to prepare for external API usage (e.g. GVT).

Also move DISPLAY_MMIO_BASE() to intel_display_device.h so it can be
abstracted in GVT, allowing register macros to resolve via
exported helpers rather than peeking into struct intel_display.

v2: Wrap the macro argument usages in parenthesis. (Jani)

Suggested-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patch.msgid.link/20251219060302.2365123-2-ankit.k.nautiyal@intel.com