drm/i915/guc: Create vfuncs for the GuC interrupts control functions

drm/i915/guc: Create vfuncs for the GuC interrupts control functions

Controlling and handling of the GuC interrupts is Gen specific.
Create virtual functions to avoid redundant runtime Gen checks.
Gen-specific versions of these functions will follow.

v2: move vfuncs to struct guc (Daniele)
v3: rebased

Signed-off-by: Oscar Mateo <oscar.mateo@intel.com>
Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.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/20190527183613.17076-12-michal.wajdeczko@intel.com