linux-imx

MAINTAINERS: Update the Allwinner sunXi entry

Chen-Yu and I have a shared git tree to host the sunxi patches now, so
let's document it.

And while we're at it, enhance our regex and document a few directories
that have been asked for in the past.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>