pinctrl: wpcm450: select MFD_SYSCON

The pinctrl-wpcm450 driver relies on MFD_SYSCON functionality in order
to find some of its MMIO registers. Select MFD_SYSCON from
PINCTRL_WPCM450 to ensure that it's enabled.

Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Link: https://lore.kernel.org/r/20230412185049.3782842-1-j.neuschaefer@gmx.net
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>