intel/isl: Codify AUX operations in an enum

intel/isl: Codify AUX operations in an enum

Right now, we have different entrypoints and enums in blorp for these
different operations.  This provides us a central enum which we can
begin to transition to.

Reviewed-by: Topi Pohjolainen <topi.pohjolainen@intel.com>
Reviewed-by: Nanley Chery <nanley.g.chery@intel.com>