fix(tsp): use VERBOSE instead of INFO

The tsp is quite vocal about what it does, however on regular DEBUG
builds this drowns out everything else. Switch the INFO statements to
VERBOSE to help combat this. tsp-ffa already does this.

Change-Id: I078f3209dc1b788f8341fbab64e8149147101aea
Signed-off-by: Boyan Karatotev <boyan.karatotev@arm.com>