dt-bindings: mmc: arm,pl18x: Make each example a separate entry

Each independent example should be a separate entry. This and dropping
'interrupt-parent' allows for 'interrupts' to have different cell sizes.

Signed-off-by: Rob Herring <robh@kernel.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20220106182518.1435497-6-robh@kernel.org