ARM: shmobile: fix smp build

I got build errors with the new version now because machine_is_kzm9g is no longer
defined:

arch/arm/mach-shmobile/platsmp.c: In function 'shmobile_smp_get_core_count':
arch/arm/mach-shmobile/platsmp.c:29:2: error: implicit declaration of function 'of_machine_is_compatible'

Replace the missing function with a call to of_machine_is_compatible.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: "Rafael J. Wysocki" <rjw@sisk.pl>
Acked-by: Magnus Damm <magnus.damm@gmail.com>