intel/isl: Add bounds-checking assertions in isl_format_get_layout

intel/isl: Add bounds-checking assertions in isl_format_get_layout

We add two assertions instead of one because the first assertion that
format != ISL_FORMAT_UNSUPPORTED is more descriptive and checks for a
real but unsupported enumerant while the second ensures that they don't
pass in garbage values.  We also update some other helpers to use
isl_format_get_layout instead of using the table directly so that they
get bounds checking too.

Cc: mesa-stable@lists.freedesktop.org
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>