arm64: dts: fvp: Add SPE to Foundation FVP

Add SPE DT node to FVP model. If the model doesn't support SPE (e.g.,
turned off via parameter), the driver will skip the initialisation
accordingly and thus is safe.

Signed-off-by: James Clark <james.clark@arm.com>
Link: https://lore.kernel.org/r/20221117102536.237515-1-james.clark@arm.com


Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>