pinctrl: PINCTRL_ROCKCHIP should depend on ARCH_ROCKCHIP

pinctrl: PINCTRL_ROCKCHIP should depend on ARCH_ROCKCHIP

The Rockchip GPIO and pin control modules are only present on Rockchip
SoCs.  Hence add a dependency on ARCH_ROCKCHIP, to prevent asking the
user about this driver when configuring a kernel without Rockchip
platform support.

Note that before, the PINCTRL_ROCKCHIP symbol was not visible, and
automatically selected when needed.  By making it tristate and
user-selectable, it became visible for everyone.

Fixes: 22d452395edcdade ("pinctrl: rockchip: make driver be tristate module")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Heiko Stuebner <heiko@sntech.de>
Link: https://lore.kernel.org/r/20210316134059.2377081-1-geert+renesas@glider.be
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>