pinctrl: mvebu: remove useless include

Including the core.h header for the pinctrl subsystem is not
necessary, and it is actually causing problems when moving the
pinctrl-mvebu drivers into a separate subdirectory.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>