ARM: dts: vexpress: use list instead of tuple for mmci interrupts

Vexpress motherboard MMCI requires dedicated interrupts for CMD and PIO,
which obviously should be expressed as a list. Current form uses tuple
and it works fine since interrupt-cells equal to 1.

Reported-by: Vladimir Murzin <vladimir.murzin@arm.com>
Reviewed-by: Vladimir Murzin <vladimir.murzin@arm.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>