Stop using builtin_run_command()

Boards can select either the 'built-in' parser or the hush parser. We
should not call builtin_run_command() if we are using the hush parser.
We use run_command() instead, since it knows how to call the correct
parser.

Signed-off-by: Simon Glass <sjg@chromium.org>
Acked-by: Mike Frysinger <vapier@gentoo.org>