drm/i915/display: add platform descriptors

We'll need to start identifying the platforms independently in display
code in order to break free from the i915 and xe IS_<PLATFORM>()
macros. This is fairly straightforward, as we already identify most
platforms by PCI ID in display probe anyway.

As the first step, add platform descriptors with pointers to display
info. We'll have more platforms than display info, so minimize
duplication:

- Add separate skl/kbl/cfl/cml descriptors while they share the display
  info.

- Add separate jsl/ehl descriptors while they share the display info.

Identify ADL-P (and derivatives) and DG2 descriptors by their names even
though their display info is Xe LPD or HPD.
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/45425c155608403efc149d4a022c0b443aa71200.1716399081.git.jani.nikula@intel.comSigned-off-by: Jani Nikula <jani.nikula@intel.com>