pinctrl: equilibrium: Add architecture dependency

The Equilibrium pin controller is only present on Intel Lightning
Mountain SoCs.  Add an architecture dependency to the
PINCTRL_EQUILIBRIUM config symbol, to avoid asking the user about it
when configuring a kernel for a non-x86 architecture.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20200507113626.24026-2-geert+renesas@glider.be


Signed-off-by: Linus Walleij <linus.walleij@linaro.org>