vexpress64.conf: disable CONFIG_CPU_IDLE to workaround boot failure

There's a known issue with ARM trusted firmware:
CPU idle does not work on the advertised version of the Foundation FVP.
Some FVP fixes are required that are not available externally at the time
of writing.

Signed-off-by: Fathi Boudra <fathi.boudra@linaro.org>
1 file changed