MAINTAINERS: demote ARM port to "odd fixes"

As of the start of 2018, I am no longer paid to support the core 32-bit
ARM architecture code.  This means that this code is no longer
commercially supported, and is now only supported through voluntary
effort.

I will continue to merge patches as and when able, but this will be at a
lower priority than before (which means a longer latency.) I have also
be scaled back the amount of time spent reading email, so email that is
intended for my attention needs to make itself plainly obvious, or I
will miss it.

In an attempt to reduce the amount of email Cc'd to me, exclude
arch/arm/boot/dts from the maintainers patterns, but add entries for the
SolidRun platforms I look after.

Link: http://lkml.kernel.org/r/E1ezkgn-0002fO-52@rmk-PC.armlinux.org.uk
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>