[util/reggen] Replace <br> with <div> wrappers
[util/reggen] Replace <br> with <div> wrappers

The reggen-generated tables don't break on <br> because that doesn't
change rendering inside of a <th>.  Wrap things that are supposed to be
distinct in <div>s to force them onto new lines.

Signed-off-by: Garret Kelly <d5e09c72d3e525ee6ce60f794290ad8eb687c905@google.com>

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