drm/xe: derive mem copy capability from graphics version

drm/xe: derive mem copy capability from graphics version

Drop .has_mem_copy_instr from the platform descriptors and set it
in xe_info_init() after handle_gmdid() populates graphics_verx100.
Centralizing the GRAPHICS_VER(xe) >= 20 check keeps MEM_COPY enabled
on Xe2+ and removes redundant per-platform plumbing.

Bspec: 57561

Fixes: 1e12dbae9d72 ("drm/xe/migrate: support MEM_COPY instruction")
Cc: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Suggested-by: Matthew Auld <matthew.auld@intel.com>
Signed-off-by: Nitin Gote <nitin.r.gote@intel.com>
Link: https://patch.msgid.link/20260120054724.1982608-2-nitin.r.gote@intel.com
Signed-off-by: Tejas Upadhyay <tejas.upadhyay@intel.com>
(cherry picked from commit 6ef02656c3222b1e12032a40d644ed56806b14fc)
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>