drm/i915/guc: Create common entry points for log register/unregister

We have many functions responsible for allocating different parts of
GuC log runtime called from multiple places. Let's stick with keeping
everything in guc_log_register instead.

v2: Use more generic intel_uc_register name, keep using "misc" suffix (Michał)
    s/dev_priv/i915 (Sagar)
    Make guc_log_relay_* static (sparse)

Signed-off-by: Michał Winiarski <michal.winiarski@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Sagar Arun Kamble <sagar.a.kamble@intel.com>
Reviewed-by: Sagar Arun Kamble <sagar.a.kamble@intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20180308154707.21716-2-michal.winiarski@intel.com