log: Convert log values to printf() if not enabled

At present if logging not enabled, log_info() becomes a nop. But we want
log output at the 'info' level to be akin to printf(). Update the macro to
pass the output straight to printf() in this case.

This mimics the behaviour for the log_...() macros like log_debug() and
log_info(), so we can drop the special case for these.

Add new tests to cover this case.
Signed-off-by: Simon Glass <sjg@chromium.org>