MAINTAINERS: update maintained files for Rockchip

MAINTAINERS: update maintained files for Rockchip

With some of the recent cleanups (e.g. moving the DRAM controller
drivers for Rockchip devices to drivers/ram/rockchip), the files
and paths listed in MAINTAINERS no longer covered what really is
looked after as part of the Rockchip port.

This commit updates the files/paths listed in MAINTAINERS for the
Rockchip port.  I am certain, though, that this will have missed some
additional paths that should have been included...

Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Acked-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>