hw/arm/spitz: Keep pointers to scp0, scp1 in SpitzMachineState

Keep pointers to scp0, scp1 in SpitzMachineState, and just pass
that to spitz_scoop_gpio_setup().

(We'll want to use some of the other fields in SpitzMachineState
in that function in the next commit.)

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-id: 20200628142429.17111-5-peter.maydell@linaro.org