patman: Add a 'test' subcommand

At present we use --test to indicate that tests should be run. It is
better to use a subcommand for list, like binman. Change it and adjust
the existing code to fit under a 'send' subcommand, the default.

Give this subcommand the same default arguments as the others.

Signed-off-by: Simon Glass <sjg@chromium.org>