FROMLIST: rpmsg: char: Add support to use rpmsg_rx_done

Add support into the rpmsg char driver to skip copying the data into an
skb if the endpoint supports rpmsg_rx_done. If the endpoint supports
the rx_done operation, allocate a zero sized skb and set the data to
the buffer returned in the rx callback. When the packet is read from
the character device, release the memory by calling rpmsg_rx_done().

Bug: 235577039
Link: https://lore.kernel.org/lkml/1654651005-15475-3-git-send-email-quic_clew@quicinc.com/


Change-Id: I5c94c560daebc4a48cee2ecfb6a44ea6c3087e8d
Signed-off-by: Chris Lew <quic_clew@quicinc.com>