drm/xe/irq: Drop unnecessary GEN11_ and GEN12_ register prefixes

drm/xe/irq: Drop unnecessary GEN11_ and GEN12_ register prefixes

Any interrupt registers that were introduced by platforms i915
considered to be "gen11" or "gen12" are present on all platforms that
the Xe driver supports; drop the unnecessary prefixes.

While working in the area, also convert a few open-coded bit
manipulations over to REG_BIT and REG_FIELD_GET notation.

Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://lore.kernel.org/r/20230401002106.588656-5-matthew.d.roper@intel.com
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
[Rodrigo: removed display. That was later squashed to the xe Display patch]