dt-bindings: imx6q-pcie: Handle more resets on legacy platforms

The i.MX6 and i.MX7D does not use block controller to toggle PCIe
reset, hence the PCIe DT description contains three reset entries
on these older SoCs. Add this exception into the binding document.

Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Marek Vasut <marex@denx.de>
Link: https://lore.kernel.org/r/20221211024859.672076-3-marex@denx.de


Signed-off-by: Rob Herring <robh@kernel.org>