drm/xe: Remove duplicate DRM_EXEC selection from Kconfig

drm/xe: Remove duplicate DRM_EXEC selection from Kconfig

There are 2 identical "select DRM_EXEC" lines for DRM_XE.
Remove one to clean up the configuration.

Fixes: d490ecf57790 ("drm/xe: Rework xe_exec and the VM rebind worker to use the drm_exec helper")
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Signed-off-by: Shuicheng Lin <shuicheng.lin@intel.com>
Reviewed-by: Nitin Gote <nitin.r.gote@intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://patch.msgid.link/20251110232657.1807998-2-shuicheng.lin@intel.com
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
(cherry picked from commit b1aa02acd03bfef3ed39c511d33c4a4303d2f9b1)
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>