intel/blorp: Add support for more format bitcasting

intel/blorp: Add support for more format bitcasting

nir_format_bitcast_uint_vec_unmasked can only be used to cast between
formats with uniform channel sizes.  In particular, it cannot handle
10_10_10_2 formats.  By making use of the NIR helper for uint vector
casts, we should now be able to bitcast between any two uint formats so
long as their channels are in RGBA order (possibly with channels
missing).  In order to do this we need to rework the key a bit to pass
the actual formats instead of just the number of bits in each.

Reviewed-by: Topi Pohjolainen <topi.pohjolainen@intel.com>