ipq806x: move common pinmux nodes to SoC DTSI

ipq806x: move common pinmux nodes to SoC DTSI

As almost same pinmux nodes are repeated in each device dts,
let's define them once in the ipq8064 dtsi and remove the rest.

* uart0_pins : Did not touch.
* i2c4_pins  : This node seems to be not used at all in dts.
               Added the most common form in the dtsi. Did not touch rpm_pins.
* spi_pins   : The common mux node is already present in the dtsi.
               Removed the duplicate nodes from dts.
* nand_pins  : Moved the entire node.
* mdio0_pins : Moved the common mux node.
* rgmii2_pins: Moved the common mux node. "pins" property is overrided in ap161.

Signed-off-by: Sungbo Eo <mans0n@gorani.run>