Created by: egrimley
Roll-back of greedy reglists was permitted even when the reglist was required to have min_num == max_num. This prevented the encoding of an instruction such as "VTBL.8 d0, {d2-d3}, d4", because it was tried with TYPE_L_VAx3 (list of length 3) before it was tried with TYPE_L_VAx2 (list of length 2). The attempt to use TYPE_L_VAx3 would incorrectly succeed because of the unrestricted roll-back.
The solution used here is to set a field reglist_min_num in the decode_info_t and disallow roll-back beyond that minimum length.
Fixes #2494 (closed)
Change-Id: Id1c22723f7862abc2cf24c0bbab4254b32232b33