There are an increasing number of ARM SoC PMU drivers appearing for
things like interconnects, memory controllers and cache controllers.
Rather than have these handled on an ad-hoc basis, where SoC maintainers
each send their PMU drivers directly to arm-soc, let's take these into
drivers/perf/ and send a single pull request to arm-soc instead, much
like other subsystems.

This patch amends the ARM PMU MAINTAINERS entry to include all of
drivers/perf/ (currently just the ARM CPU PMU), changes Mark Rutland
from Reviewer to Maintainer, so that he can help with the new tree and
adds the device-tree binding to the list of maintained files.
Acked-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Will Deacon <will.deacon@arm.com>