ARM: 6895/1: mach-ux500: fix SMP secondary startup regression

Commit e2a083dc0da9aa6437e14811198379b18cdfa7f8
"ARM: consolidate SMP cross call implementation" broke the ux500
compilation since the smp.h header declared a function called
from headsmp.S. This fixes it up by declaring it locally instead.
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/mach-ux500/platsmp.c

@@ -23,6 +23,9 @@
 #include <mach/hardware.h>
 #include <mach/setup.h>
 
+/* This is called from headsmp.S to wakeup the secondary core */
+extern void u8500_secondary_startup(void);
+
 /*
  * control for which core is the next to come out of the secondary
  * boot "holding pen"