Make sure we always have CT buffers enabled when the interrupts are
enabled, so we can always handle interrupts from GuC. Also move the
setting of the guc->send and guc->handler functions to the GuC
communication control functions for consistency.

The reorder also fixes the onion unwinding of intel_uc_init_hw, because
guc_enable_communication would've left interrupts enabled when failing
to enable CTB.

v2: always retunr the result of ctch_enable() in
    intel_guc_ct_enable() (Michal)

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=110943Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Michal Wajdeczko <michal.wajdeczko@intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20190621182123.31368-1-daniele.ceraolospurio@intel.com