arm: vexpress: Remove obsolete RTSM DCSCB support

The Arm Versatile DCSCB support is unused as the compatible
"arm,rtsm,dcscb" is unused in any .dts file. It was only ever
implemented on a s/w model (RTSM).

Signed-off-by: Rob Herring (Arm) <robh@kernel.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20240510123238.3904779-1-robh@kernel.org


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