dt-bindings: net: motorcomm: Add pad driver strength cfg

The motorcomm phy (YT8531) supports the ability to adjust the drive
strength of the rx_clk/rx_data.

The YT8531 RGMII LDO voltage supports 1.8V/3.3V, and the
LDO voltage can be configured with hardware pull-up resistors to match
the SOC voltage (usually 1.8V). The software can read the registers
0xA001 obtain the current LDO voltage value.

Reviewed-by: Hal Feng <hal.feng@starfivetech.com>
Signed-off-by: Samin Guo <samin.guo@starfivetech.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: David S. Miller <davem@davemloft.net>