cpu: Register a generic CPU device on architectures that currently do not

frv, h8300, m68k, microblaze, openrisc, score, um and xtensa currently
do not register a CPU device.  Add the config option GENERIC_CPU_DEVICES
which causes a generic CPU device to be registered for each present CPU,
and make all these architectures select it.

Richard Weinberger <richard@nod.at> covered UML and suggested using
per_cpu.

Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/arch/h8300/Kconfig b/arch/h8300/Kconfig
index d1f377f..56e890d 100644
--- a/arch/h8300/Kconfig
+++ b/arch/h8300/Kconfig
@@ -4,6 +4,7 @@
 	select HAVE_IDE
 	select HAVE_GENERIC_HARDIRQS
 	select GENERIC_IRQ_SHOW
+	select GENERIC_CPU_DEVICES
 
 config SYMBOL_PREFIX
 	string