drm/i915/guc: Use intel_guc_init_misc to hide GuC internals

We will add more init steps to misc phase and there is no need
to expose them separately for use in uc_init_misc function.

Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Michel Thierry <michel.thierry@intel.com>
Reviewed-by: Michel Thierry <michel.thierry@intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20180628141522.62788-1-michal.wajdeczko@intel.com