drm/xe/irq: Rename and clarify top-level interrupt handling routines

Platforms supported by the Xe driver handle top-level interrupts in one
of two ways:
 - Xe_LP platforms only have a "graphics master" register and lack a
   "master tile" register, so top-level interrupt detection and
   enable/disable happens in the graphics master.
 - Xe_LP+ (aka DG1) and beyond have a "master tile" interrupt register
   that controls the enable/disable of top-level interrupts and must
   also be consulted to determine which tiles have received interrupts
   before the driver moves on the process the graphics master register.

For functions that are only relevant to the first set of platforms,
rename the function prefix to Xe_LP since "gen11" doesn't make sense in
the Xe driver.  Also add some comments briefly describing the two
top-level handlers.

Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://lore.kernel.org/r/20230401002106.588656-6-matthew.d.roper@intel.com


Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>