drm/i915/xe2lpd: Move registers to PICA

Some registers for DDI A/B moved to PICA and now follow the same format
as the ones for the PORT_TC ports. The wrapper here deals with 2 issues:

	- Share the implementation between xe2lpd and previous
	  platforms: there are minor layout changes, it's mostly the
	  register location that changed
	- Handle offsets after TC ports

v2:
  - Explain better the trick to use just the second range (Matt Roper)
  - Add missing conversions after rebase (Matt Roper)
  - Use macro instead of inline function, avoiding includes in the
    header (Jani)
  - Prefix old macros with underscore so they don't get used by mistake,
    and name the new ones using the previous names
v3: Use the same logic for the recently-introduced XELPDP_PORT_MSGBUS_TIMER
    (Gustavo)

Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Gustavo Sousa <gustavo.sousa@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240126224638.4132016-3-lucas.demarchi@intel.com