rockchip: pinctrl: rk3368: move IOMUX bit-definitions to pinctrl driver

rockchip: pinctrl: rk3368: move IOMUX bit-definitions to pinctrl driver

There is no real reason to keep the bit-definitions for the IOMUX in
the grf header file (which defines the register layout of the GRF block):
these should only be used by our pinctrl driver (with the possible
exception of early debug-init code in TPL/SPL).

This moves the relevant definitions from the grf_rk3368.h header
into the pinctrl driver pinctrl_rk3368.c.

Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Reviewed-by: Simon Glass <sjg@chromium.org>