fix(measured-boot): fix verbosity level of RSS digests traces

Most traces displayed by log_measurement() use the INFO verbosity
level. Only the digests are unconditionally printed, regardless of
the verbosity level. As a result, when the verbosity level is set
lower than INFO (typically in release mode), only the digests are
printed, which look weird and out of context.

Change-Id: I0220977c35dcb636f1510d8a7a0a9e3d92548bdc
Signed-off-by: Sandrine Bailleux <sandrine.bailleux@arm.com>