Add definition for block 56, the compression parameters.

v2: add missing slice_height (Vandita)

Cc: Vandita Kulkarni <vandita.kulkarni@intel.com>
Reviewed-by: Vandita Kulkarni <vandita.kulkarni@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191024075608.11511-1-jani.nikula@intel.com