intel: decoder: build sorted linked lists of fields

intel: decoder: build sorted linked lists of fields

The xml files don't always have fields in order. This might confuse
our parsing of the commands. Let's have the fields in order. To do
this, the easiest way it to use a linked list. It also helps a bit
with the iterator.

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Scott D Phillips <scott.d.phillips@intel.com>