I've seen people increasing the compile loglevel to get more debugging
output from barebox. This is generally a good idea, but the tons of hush
debugging printed makes barebox quite unusable. This patch puts hush
debugging behind an extra HUSH_DEBUG define so increasing the compile
loglevel no longer results in hush debugging.

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