drm/xe: Add fault injection for xe_oa_alloc_regs

drm/xe: Add fault injection for xe_oa_alloc_regs

Add fault injection for xe_oa_alloc_regs to allow it to fail while
executing xe_oa_add_config_ioctl().
This need to be added as it cannot be reached by injecting error through
IOCTL arguments.

Signed-off-by: Nakshtra Goyal <nakshtra.goyal@intel.com>
Reviewed-by: Francois Dugast <francois.dugast@intel.com>
Reviewed-by: Himal Prasad Ghimiray <himal.prasad.ghimiray@intel.com>
Link: https://lore.kernel.org/r/20250227102339.2859726-1-nakshtra.goyal@intel.com
Signed-off-by: Himal Prasad Ghimiray <himal.prasad.ghimiray@intel.com>