arm: mach-k3: security: Lower verbosity of cert message for GP

When we find a certificate on an image to be booted on a GP device we
print out a message explaining that the certificate is being skipped.
This message is rather long and is printed for every image. Shorten
the message and make the long version into a debug message.

Signed-off-by: Andrew Davis <afd@ti.com>
Tested-by: Jonathan Humphreys <j-humphreys@ti.com>