This allows the basic registers of the general register files to be supplied
by a syscon instead of being mapped locally.

The GRF registers contain a lot more than pinctrl functions like dma, usb-phy
and general soc control and status registers, intermixed with the iomux, pull
and drive-strength registers.
Signed-off-by: NHeiko Stuebner <heiko@sntech.de>
Tested-by: NMax Schwarz <max.schwarz@online.de>
Signed-off-by: NLinus Walleij <linus.walleij@linaro.org>