remoteproc/davinci: Add device tree support for OMAP-L138 DSP

The Davinci remoteproc driver currently supports the DSP remoteproc
device created in legacy-style on OMAP-L13x SoCs. The driver has been
enhanced to support the DSP remoteproc device created through Device
Tree now. The current DT support handles the C674x DSP processor
subsystem on OMAP-L138 SoCs.

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