Existing macro ERROR() prints string "ERROR" followed by string
specified by caller. Therefore via this existing macro it is not
possible to end incomplete / existing line by a newline character.

This change adds a new macro ERROR_NL() which prints just a newline
character without any prefix. Implementation of this macro is done via a
new function tf_log_newline() which based on supplied log level either
return or print newline character.

If needed in future based on this tf_log_newline() function can be
defined also macros for other log levels.
Signed-off-by: Pali Rohár <pali@kernel.org>
Change-Id: I05414ca177f94cdc0f6077394d9c4af4a4382306