pinctrl: sh-pfc: rename confusing pinmux ops variable

The vtable named *pinmux_ops in the affected files are not really
about pin multiplexing, but a struct related to some PFC-specific
operations, inclusing pin config (bias setting). Rename the variable
so as to avoid confusions.

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