fix(spm): change error logs to verbose

Helper functions to validate return of FF-A calls or responses
from other endpoints in 'spm_common', were printing ERROR also in cases
where this was actually expected.
Changing those ERROR messages to VERBOSE, given ERROR as referred was
misleading.

Signed-off-by: J-Alves <joao.alves@arm.com>
Change-Id: Id3feac197e8dbff78a616392b5ac7ca914c219df
1 file changed