dt-bindings: mhi: mhi netdev no longer support recycle memory

Recycle memory is no longer supported by Linux rmnet network
solution. Therefore, we have remove support from MHI network
layer. Updating device tree documentation to reflect driver
changes.

CRs-Fixed: 2325839
Change-Id: I1d9274449e9033ac8fefdc3aae3a5aae0dc32c96
Signed-off-by: Sujeev Dias <sdias@codeaurora.org>