pinctrl: meson: fix uart_ao_b for GXBB and GXL/GXM

pinctrl: meson: fix uart_ao_b for GXBB and GXL/GXM

The GXBB and GXL/GXM pinctrl drivers had a configuration which conflicts
with uart_ao_a. According to the GXBB ("S905") datasheet the AO UART
functions are:
- GPIOAO_0: Func1 = UART_TX_AO_A (bit 12), Func2 = UART_TX_AO_B (bit 26)
- GPIOAO_1: Func1 = UART_RX_AO_A (bit 11), Func2 = UART_RX_AO_B (bit 25)
- GPIOAO_4: Func2 = UART_TX_AO_B (bit 24)
- GPIOAO_5: Func2 = UART_RX_AO_B (bit 25)

The existing definition for uart_AO_A already uses GPIOAO_0 and GPIOAO_1.
The old definition of uart_AO_B however was broken, as it used GPIOAO_0
for TX (which would be fine) and two pins (GPIOAO_1 and GPIOAO_5) for RX
(which does not make any sense).

This fixes the uart_AO_B configuration by moving it to GPIOAO_4 and
GPIOAO_5 (it would be possible to use GPIOAO_0 and GPIOAO_1 in theory,
but all existing hardware uses uart_AO_A there).
The fix for GXBB and GXL/GXM is identical since it seems that these
specific pins are identical on both SoC variants.

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Reviewed-by: Kevin Hilman <khilman@baylibre.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>