arm64: defconfig: enable SENSORS_ARM_SCPI

ARM SCPI Sensors were merged for v4.4 and they are defined in the Juno
dts.  Enable it in the defconfig to get them registered automatically in
Juno by default.

Signed-off-by: Javi Merino <javi.merino@arm.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>