Add PBL console support ...

This adds simple console support to the PBL which makes it
possible to print more complex messages in the PBL than just
strings or hex numbers. For now puts_ll is used to print the
messages, so it depends on CONFIG_DEBUG_LL which makes it
more a debugging option. However, this could be extended later
to get regular output from the PBL if desired.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>