drm/i915: Sanitize open-coded power well enable()/disable() calls

Instead of open-coding the call of the power wells' enable()/disable()
hooks use the corresponding helper functions. This will also ensure that
the power well's cached-enable state is always up-to-date. Luckily the
lack of this updating hasn't been a problem, since the state either
didn't change (in intel_display_power_set_target_dc_state()), or got
updated subsequently (for vlv_cmnlane_wa(), in the following
intel_power_domains_sync_hw()).

Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Jouni Högander <jouni.hogander@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220222165137.1004194-3-imre.deak@intel.com