soc: rockchip: add driver handling grf setup

The General Register Files are an area of registers containing a lot
of single-bit settings for numerous components as well full components
like usbphy control. Therefore all used components are accessed
via the syscon provided by the grf nodes or from the sub-devices
created through the simple-mfd created from the grf node.

Some settings are not used by anything but will need to be set up
according to expectations on the kernel side.

Best example is the force_jtag setting, which defaults to on and
results in the soc switching the pin-outputs between jtag and sdmmc
automatically depending on the card-detect status. This conflicts
heavily with how the dw_mmc driver expects to do its work and also
with the clock-controller, which has most likely deactivated the
jtag clock due to it being unused.

So far the handling of this setting was living in the mach-rockchip
code for the arm32-based rk3288 but that of course doesn't work
for arm64 socs and would also look ugly for further arm32 socs.

Also always disabling this setting is quite specific to linux and
its subsystems, other operating systems might prefer other settings,
so that the bootloader cannot really set a sane default for all.

So introduce a top-level driver for the grf that handles these
settings that need to be a certain way but nobody cares about.

Other needed settings might surface in the future and can then
be added here, but only as a last option. Ideally general GRF
settings should be handled in the driver needing them.

Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Reviewed-by: Douglas Anderson <dianders@chromium.org>

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