Gigabit Ethernet requires the Ethernet TXD0..3 and RXD0..3 data lines.
Add the missing eth_rxd2 and eth_rxd3 definitions so we don't have to
rely on the bootloader to set them up correctly.

The vendor u-boot sources for Odroid-C1 use the following Ethernet
pinmux configuration:
  SET_CBUS_REG_MASK(PERIPHS_PIN_MUX_6, 0x3f4f);
  SET_CBUS_REG_MASK(PERIPHS_PIN_MUX_7, 0xf00000);
This translates to the following pin groups in the mainline kernel:
- register 6 bit  0: eth_rxd1 (DIF_0_P)
- register 6 bit  1: eth_rxd0 (DIF_0_N)
- register 6 bit  2: eth_rx_dv (DIF_1_P)
- register 6 bit  3: eth_rx_clk (DIF_1_N)
- register 6 bit  6: eth_tx_en (DIF_3_P)
- register 6 bit  8: eth_ref_clk (DIF_3_N)
- register 6 bit  9: eth_mdc (DIF_4_P)
- register 6 bit 10: eth_mdio_en (DIF_4_N)
- register 6 bit 11: eth_tx_clk (GPIOH_9)
- register 6 bit 12: eth_txd2 (GPIOH_8)
- register 6 bit 13: eth_txd3 (GPIOH_7)
- register 7 bit 20: eth_txd0_0 (GPIOH_6)
- register 7 bit 21: eth_txd1_0 (GPIOH_5)
- register 7 bit 22: eth_rxd3 (DIF_2_P)
- register 7 bit 23: eth_rxd2 (DIF_2_N)

All functions except eth_rxd2 and eth_rxd3 are already supported by the
pinctrl-meson8b driver.
Suggested-by: Jianxin Pan <jianxin.pan@amlogic.com>
Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Reviewed-by: Kevin Hilman <khilman@baylibre.com>
Tested-by: Emiliano Ingrassia <ingrassia@epigenesys.com>
Reviewed-by: Emiliano Ingrassia <ingrassia@epigenesys.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>