MAINTAINERS: Update ARM PMU PROFILING AND DEBUGGING entry

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>