drm/i915/guc: Rename intel_guc_is_alive to intel_guc_is_loaded

This function just check our software flag, while 'is_alive'
may suggest that we are checking runtime firmware status.

Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20190522193203.23932-5-michal.wajdeczko@intel.com