Register 0x9424 is not replicated on any platform, so it shouldn't be
declared with REG_MCR(). Declaring it with _MMIO() is basically
duplicate of the GEN7 version, so just remove the GEN8 and change all
the callers to use the right functions.

Old versions of the gen8 bspec page used to contain a table with MCR
registers, apparently implying 0x9400 - 0x94ff registers were
replicated. However that table went away and there is no information
related to the ranges for gen8 anymore. Moreover the current behavior of
the driver wouldn't do anything special for 0x9424 since there is no
equivalent table in intel_gt_mcr.c: the driver would just fallback to
intel_uncore_{read,write}(). Therefore, do not care about the possible
special case for gen8 and just use the register as non-MCR for all the
platforms.

One place doing read + write is also converted to intel_uncore_rmw().

v2: Reword commit message adding the justification wrt gen8

Fixes: a9e69428 ("drm/i915: Define MCR registers explicitly")
Cc: Balasubramani Vivekanandan <balasubramani.vivekanandan@intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Gustavo Sousa <gustavo.sousa@intel.com>
Cc: Matt Atwood <matthew.s.atwood@intel.com>
Cc: Ashutosh Dixit <ashutosh.dixit@intel.com>
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230206165410.3056073-1-lucas.demarchi@intel.com