fiptool: print new lines of usage to stdout instead of stderr

fiptool: print new lines of usage to stdout instead of stderr

The strings in usage functions are sent to stdout by printf(),
but some new lines are sent to stderr by fputc(..., stderr).

This inconsistency will break the usage format when users re-direct
stdout or stderr.  Just use printf() for consistency.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>