drm/xe: Compute dumb-buffer sizes with drm_mode_size_dumb()

drm/xe: Compute dumb-buffer sizes with drm_mode_size_dumb()

Call drm_mode_size_dumb() to compute dumb-buffer scanline pitch
and buffer size. Align the pitch to a multiple of 8. Align the
buffer size according to hardware requirements.

Xe's internal calculation allowed for 64-bit wide buffer sizes, but
the ioctl's internal checks always verified against 32-bit wide limits.
Hance, it is safe to limit the driver code to 32-bit calculations as
well.

v3:
- mention 32-bit calculation in commit description (Matthew)

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Acked-by: Lucas De Marchi <lucas.demarchi@intel.com>
Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Cc: "Thomas Hellström" <thomas.hellstrom@linux.intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://lore.kernel.org/r/20250821081918.79786-24-tzimmermann@suse.de