Even if the log output is too low for a message to be printed out on
the console by the debug macros, it should still be evaluated by the
compiler to get some type checking and validation of the format
specifiers. To do so, introduce the no_tf_log() macro that encloses
the call to tf_log() in an always-false condition.

This avoids the problem of discovering build issues only when we build
the firmware with the right LOG_LEVEL value.

Change-Id: Ic0fd252ab691d0187fd925756a4837aca1cbfd7b
Signed-off-by: Sandrine Bailleux <sandrine.bailleux@arm.com>