Once again ILK is unhappy if we clear out the LP1+ watermark levels
outright, and instead we must disable the levels we don't want while
still leaving the actual programmed watermark levels intact.

Fixes underruns on the already enabled pipe when programming watermarks
while enabling the second pipe.

Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Matt Roper <matthew.d.roper@intel.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=93787Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1459536799-18109-3-git-send-email-ville.syrjala@linux.intel.comReviewed-by: Patrik Jakobsson <patrik.jakobsson@linux.intel.com>