pinctrl: pinctrl-aspeed-g6: add FWQSPI function-group

Add FWSPIDQ2 (AE12) and FWSPIDQ3 (AF12) function-group to support
AST2600 FW SPI quad mode. These pins can be used with dedicated FW
SPI pins - FWSPICS0# (AB14), FWSPICK (AF13), FWSPIMOSI (AC14)
and FWSPIMISO (AB13).

Signed-off-by: Johnny Huang <johnny_huang@aspeedtech.com>
Signed-off-by: Jae Hyun Yoo <quic_jaehyoo@quicinc.com>
Reviewed-by: Andrew Jeffery <andrew@aj.id.au>
Link: https://lore.kernel.org/r/20220329173932.2588289-5-quic_jaehyoo@quicinc.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>