RISC-V: Add placeholder for the "B" extension

The "B" extension is once abandoned (instead, it is ratified as a collection
of "Zb*" extensions).  However, it is later redefined and ratified as a
superset of "Zba", "Zbb" and "Zbs" extensions (but not "Zbc" carry-less
multiplication for limited benefits and implementation cost).

Although non-functional (because feature detection is not yet implemented),
it provides the foundation to implement this extension (along with
straightforward documentation showing subsets of "B").

0 files changed, 0 insertions, 0 deletions