dt-bindings: remoteproc: Add bindings for R5F subsystem on TI K3 SoCs

The Texas Instruments K3 family of SoCs have one or more dual-core
Arm Cortex R5F processor subsystems/clusters (R5FSS). The clusters
can be split between multiple voltage domains as well. Add the device
tree bindings document for these R5F subsystem devices. These R5F
processors do not have an MMU, and so require fixed memory carveout
regions matching the firmware image addresses. The nodes require more
than one memory region, with the first memory region used for DMA
allocations at runtime. The remaining memory regions are reserved
and are used for the loading and running of the R5F remote processors.
The R5F processors can also optionally use any internal on-chip SRAM
memories either for executing code or using it as fast-access data.

The added example illustrates the DT nodes for the single R5FSS device
present on K3 AM65x family of SoCs.
Signed-off-by: Suman Anna <s-anna@ti.com>
Link: https://lore.kernel.org/r/20201002234234.20704-2-s-anna@ti.comSigned-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>