docs(maintainers): add Julius Werner as Rockchip platform code owner
docs(maintainers): add Julius Werner as Rockchip platform code owner

The two existing plat/rockchip code owners seem to be no longer active
in the project and are not responding to reviews. There have been a
couple of small fixup patches[1][2][3] pending for months that couldn't
be checked in for lack of Code-Owner-Review+1 flag. Add myself to the
code owner list to unblock this bottleneck (I have been deeply involved
in the rk3399 port, at least, so I know most of the code reasonably
well).

[1] https://review.trustedfirmware.org/9616
[2] https://review.trustedfirmware.org/9990
[2] https://review.trustedfirmware.org/10415

Signed-off-by: Julius Werner <4d12f06cff3725783b352157673a720bc67c4afe@chromium.org>
Change-Id: Ic7b2bb73c35a9bea91ff46ee445a22819d2045d9

achingupta/arm-trusted-firmware,achingupta/arm-trusted-firmware