drm/i915/uc: Add ops to intel_uc

Instead of spreading multiple conditionals across the uC code
to find out current mode of uC operation, start using predefined
set of function pointers that reflect that mode.

Begin with pair of init_hw/fini_hw functions that are responsible
for uC hardware initialization and cleanup.

v2: drop ops_none, use macro to generate ops helpers
v3: reuse __uc_check_hw to avoid redundant comment
v4: forward declare ops struct vs functions

Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.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/20200110222723.14724-2-michal.wajdeczko@intel.com