drm/xe/oa: Remove WARN_ON's for unsupported configurations

The OA ioctl's already have drm_dbg's which are sufficient to tell the user
that OA is not supported on unsupported configurations (execlist mode and
platform gen < 12). Having additional WARN_ON's for these during driver
probe create unnecessary noise. Just remove these WARN_ON's.

Suggested-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Signed-off-by: Ashutosh Dixit <ashutosh.dixit@intel.com>
Reviewed-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240619225617.3465899-1-ashutosh.dixit@intel.com