[otbn,dv] Allow maximal size LOOPIs in RIG
[otbn,dv] Allow maximal size LOOPIs in RIG

This commit splits apart the code that chooses a number of iterations
for LOOP and LOOPI instructions, then changes the distribution of
LOOPI values. In particular, we now allow the RIG to occasionally
generate a loop with 1023 iterations (hitting a coverage point for
maximal value of an operand).

Signed-off-by: Rupert Swarbrick <290093e2ad2515ed2f14d749293c8cf8e02ca274@lowrisc.org>

lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan