drm/i915: Change watermark hook calling convention

Just pass the atomic_state+crtc to the watermarks hooks. Eeasier
time for the caller when it doesn't have to think what to pass.

Reviewed-by: Manasi Navare <manasi.d.navare@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191118164430.27265-7-ville.syrjala@linux.intel.com