dt-bindings: qdsp: device-tree documentation for CDSP loader

Device-tree documentation for the CDSP loader driver node which
enables loading of firmware images and bringing the subsystem out
of reset during boot-up.

Change-Id: I9625873a51583aa5594b88e434c9ac423eaf0e78
Acked-by: Thyagarajan Venkatanarayanan <venkatan@qti.qualcomm.com>
Signed-off-by: Tharun Kumar Merugu <mtharu@codeaurora.org>