drm/xe: Make PPHWSP size explicit in xe_gt_lrc_size()

drm/xe: Make PPHWSP size explicit in xe_gt_lrc_size()

The context of each engine starts with a 4k memory space for the
"Per-process HW status page" (PPHWSP). In xe_gt_lrc_size(), we have been
implicitly accounting for that page in the switch statement on the
engine class.

Since the PPHWSP is common to all engines, let's extract that into it's
own assignment. That makes the context structure more explicit in the
code and aligns better with the descriptions in Bspec.

Another advantage of keeping it separate is that now the sizes used in
the switch statement match the sizes we calculate engine-specific
context images, which have their own Bspec pages.

Bspec: 67296, 60159, 45554
Signed-off-by: Gustavo Sousa <gustavo.sousa@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://lore.kernel.org/r/20250328-explicit-pphwsp-size-in-xe_gt_lrc_size-v1-1-ceb9ce7c8bc1@intel.com
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>