arm: convert to generic helpers for IPI function calls

This converts arm to use the new helpers for smp_call_function() and
friends, and adds support for smp_call_function_single().

Fixups and testing done by Catalin Marinas <catalin.marinas@arm.com>

Cc: Russell King <rmk@arm.linux.org.uk>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index b786e68..c72dae6 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -650,6 +650,7 @@
 config SMP
 	bool "Symmetric Multi-Processing (EXPERIMENTAL)"
 	depends on EXPERIMENTAL && (REALVIEW_EB_ARM11MP || MACH_REALVIEW_PB11MP)
+	select USE_GENERIC_SMP_HELPERS
 	help
 	  This enables support for systems with more than one CPU. If you have
 	  a system with only one CPU, like most personal computers, say N. If