This patch fixes the PLAT_LOG_LEVEL_ASSERT to 40 which corresponds
to LOG_LEVEL_INFO. Having this level of log for assertions means that the
`assert()` will not generate the strings implied in the expression taken
as parameter. This allows to save some memory when Juno is built for
LOG_LEVEL = LOG_LEVEL_VERBOSE and DEBUG = 1.

Fixes ARM-software/tf-issues#511

Change-Id: Id84a40f803ab07a5a8f6e587167af96694a07d04
Signed-off-by: Soby Mathew <soby.mathew@arm.com>