dt-bindings: remoteproc: k3-dsp: Update bindings for C71x DSPs

Some Texas Instruments K3 family of SoCs have one of more newer
generation TMS320C71x CorePac processor subsystem in addition to
the existing TMS320C66x CorePac processor subsystems. Update the
device tree bindings document for the C71x DSP devices.

The example is also updated to show the single C71 DSP present
on J721E SoCs.

Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Suman Anna <s-anna@ti.com>
Link: https://lore.kernel.org/r/20200612225357.8251-2-s-anna@ti.com
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>