sh-pfc: Use GPIO_FN instead of PINMUX_GPIO where possible

The GPIO_FN macro expands to the PINMUX_GPIO macro. The regular
expression to 'unexpand' PINMUX_GPIO to GPIO_FN is

s/\tPINMUX_GPIO(GPIO_FN_\([A-Z0-9_]*\),[ \t]*\1_MARK)/\tGPIO_FN(\1)/

This consolidates SoC-specific PFC information to use the same macros
for all SoCs.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>