drm/i915/display: add platform member to struct intel_display

drm/i915/display: add platform member to struct intel_display

Facilitate using display->platform.haswell and
display->platform.haswell_ult etc. for identifying platforms and
subplatforms.

Merge the platform and subplatform bitmaps together, and check that
there's no overlap.

v4:
- Lower case, s/is/platform/

v3:
- Fix sanity check on display->is after merging subplatform members

v2:
- Use bitmap ops
- Add some sanity checks with warnings

Reviewed-by: Rodrigo Vivi <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/2ae79637390372903a9808b5adc4d2dcf2c5959b.1730144869.git.jani.nikula@intel.com
Signed-off-by: Jani Nikula <[email protected]>