drm/xe/tests: Remove CONFIG_FB dependency

We currently don't have any tests that explicitly depends on this
config option, so remove that build dependency.

Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>