west: sign.py: always log the rimage command

rimage is very verbose by default and has no -q(uiet) option, so saving
one line out of more than 100 lines is pointless.

RimageSigner.sign() was already very complex and suffering from
combinatorial explosion of parameters. With .toml
pre-processing (#65411) it's getting worse, so we really need all build
logs to show the complete rimage command.

Signed-off-by: Marc Herbert <marc.herbert@intel.com>