mfd: mt6397-core: Add resources for PMIC keys for MT6359

Add the MFD resources in order to be able to probe and use the keyboard
driver for the MT6359 PMIC.

Signed-off-by: Fabien Parent <fparent@baylibre.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20220415153629.1817202-4-fparent@baylibre.com