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>
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 1c50210..4f7bc3d 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -1701,12 +1701,8 @@
 	  user-space 2nd level page tables to reside in high memory.
 
 config HW_PERF_EVENTS
-	bool "Enable hardware performance counter support for perf events"
-	depends on PERF_EVENTS
-	default y
-	help
-	  Enable hardware performance counter support for perf events. If
-	  disabled, perf events will use software events only.
+	def_bool y
+	depends on ARM_PMU
 
 config SYS_SUPPORTS_HUGETLBFS
        def_bool y