Fixed decoding of various Hint instructions

Created by: Silabs-ArjanB

Implemented hint instructions (behaving as NOPs).

This solves issue #116 (closed) and it also implements missing hints as nops for the following other instructions according to the RISC-V Unprivileged spec:

• c.add (handling hint as nop instead of generating illegal instruction exception) (issue #116 (closed))
• c.li (handling hint as nop instead of generating illegal instruction exception)
• c.lui (handling hint as nop instead of generating illegal instruction exception)
• c.slli (handling hint as nop instead of generating illegal instruction exception)
• c.slli64 (handling hint as nop instead of generating illegal instruction exception)
• c.srli64 (handling hint as nop instead of generating illegal instruction exception)
• c.srai64 (handling hint as nop instead of generating illegal instruction exception)

c.nop and c.addi were already okay. c.mv was okay as well, but code was restructured to make it more obvious that we took hints into account.

Signed-off-by: Arjan Bink Arjan.Bink@silabs.com