arm: perf: factor arm_pmu core out to drivers

To enable sharing of the arm_pmu code with arm64, this patch factors it
out to drivers/perf/. A new drivers/perf directory is added for
performance monitor drivers to live under.

MAINTAINERS is updated accordingly. Files added previously without a
corresponsing MAINTAINERS update (perf_regs.c, perf_callchain.c, and
perf_event.h) are also added.

Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
[will: augmented Kconfig help slightly]
Signed-off-by: Will Deacon <will.deacon@arm.com>

drivers/perf/Kconfig

@@ -0,0 +1,15 @@
+#
+# Performance Monitor Drivers
+#
+
+menu "Performance monitor support"
+
+config ARM_PMU
+	depends on PERF_EVENTS && ARM
+	bool "ARM PMU framework"
+	default y
+	help
+	  Say y if you want to use CPU performance monitors on ARM-based
+	  systems.
+
+endmenu