drm/i915/guc: Extract guc_init from guc_init_hw

After GPU reset, GuC HW needs to be reinitialized (with FW reload).
Unfortunately, we're doing some extra work there (mostly allocating stuff),
work that can be moved to guc_init and called once at driver load time.

As a side effect we're no longer hitting an assert in
i915_ggtt_enable_guc on suspend/resume.

v2: Do not duplicate disable_communication / reset_guc_interrupts
v3: Add proper teardown after rebase

References: 04f7b24e ("drm/i915/guc: Assert that we switch between known ggtt->invalidate functions")
Signed-off-by: Michał Winiarski <michal.winiarski@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Sagar Arun Kamble <sagar.a.kamble@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/20171213221352.7173-3-michal.winiarski@intel.com