drm/i915/display: add display platforms structure with platform members

drm/i915/display: add display platforms structure with platform members

Add a structure with a bitfield member for each platform and
subplatform, and initialize them in platform and subplatform descs.

The structure also contains a bitmap in a union for easier manipulation
of the bits. This, in turn, requires a bit of trickery with
INTEL_DISPLAY_PLATFORMS() to count the number of bits required for
DECLARE_BITMAP().

Reviewed-by: Rodrigo Vivi <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/bf1d828cd333d34862ad3198e282c9d294c6e1ad.1730144869.git.jani.nikula@intel.com
Signed-off-by: Jani Nikula <[email protected]>