drm/i915/guc: Preparing for GuC reset along with engine reset

Adding the call to prepare for guc reset along with engine
reset. intel_uc_reset_prepare() calls to disable guc communication
and to sanitize.

Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Michal Wajdeczko <michal.wajdeczko@intel.com>
Signed-off-by: Sujaritha Sundaresan <sujaritha.sundaresan@intel.com>
Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20190307184445.25895-1-sujaritha.sundaresan@intel.com