Following f3ccf036ecb1ae1628 the INFO print in amu_enable is causing
a lot of print outs on UART1 in DEBUG mode especially on PSCI test
cases because CPU_ON or SUSPEND operations call:
cm_prepare_el3_exit => enable_extensions_nonsecure => amu_enable.
PSCI SUSPEND is also very frequent in linux boot cases causing test
timeout failures.

Signed-off-by: Olivier Deprez <olivier.deprez@arm.com>
Change-Id: I63581f8fa489d44b3b1d10af3b7f6fdf3af44720