rockchip: rk3368: dts: add DMC node in rk3368.dtsi

rockchip: rk3368: dts: add DMC node in rk3368.dtsi

For full SPL support, including DRAM initialisation, we need a few
nodes from the DTS: this commit adds the DMC (DRAM controller) node,
the service_msch (memory scheduler) node and marks GRF, PMUGRF and CRU
as 'u-boot,dm-pre-reloc'.  In addition to this, we also include the
dt-binding for the DMC to allow DTS files including this DTSI to refer
to the symbolic constants for the DDR3 bin and for the
memory-schedule.

Note that the DMC contains both the memory regions for the
(Designware) protocol controller as well as the DDR PHY.

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