rpmsg: Add snapshot of RPMSG Glink drivers

This snapshot is taken as of msm-4.14 'commit <67942dbf>
("Merge "net: netfilter: IRC DCC for private clients"")'.

This change brings the rpmsg and rpmsg glink drivers up to date with
the fixes from msm-4.14 and also adds the spi and spss transports from
msm-4.14. In addition, change the copyrights to SPDX format.

Change-Id: Idc0c9ad00c0562a7f3e2807ea9cfca644680dd9d
Signed-off-by: Chris Lew <clew@codeaurora.org>