gpio: vr41xx: Delete vr41xx_gpio_pullupdown() callback

This API is not used anywhere in the kernel and has remained
unused for years after being introduced.

Over time, we have developed a subsystem to deal with pin
control and this now managed pull up/down.

Delete the old and unused API. If this platform needs it,
we should implement a proper pin controller for it instead.

Cc: Yoichi Yuasa <yuasa@linux-mips.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Acked-by: Paul Burton <paul.burton@mips.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>