Now that the ARM CCI PMU driver can be built as a loadable module,
we get a link failure when MCPM is enabled:

ERROR: "mcpm_is_available" [drivers/perf/arm-cci.ko] undefined!

The simplest fix is to export that helper function.

Fixes: 8b0c93c2 ("perf/arm-cci: Allow building as a module")
Acked-by: NNicolas Pitre <nico@linaro.org>
Acked-by: NRussell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: NArnd Bergmann <arnd@arndb.de>
Signed-off-by: NWill Deacon <will.deacon@arm.com>