dt-bindings: remoteproc: Add bindings for Davinci DSP processors

Add the device tree bindings document for the DSP processor
subsystem devices on TI Davinci DA8xx/OMAP-L13x SoCs.

Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Suman Anna <s-anna@ti.com>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>