ARM: versatile: fix missing <plat/platsmp.h> include

Fix two missing function declarations by including the
<plat/platsmp.h> file where they are defined. Fixes:

arch/arm/plat-versatile/platsmp.c:35:6: warning: symbol 'versatile_secondary_init' was not declared. Should it be static?
arch/arm/plat-versatile/platsmp.c:50:5: warning: symbol 'versatile_boot_secondary' was not declared. Should it be static?

Cc: Liviu Dudau <[e-mail]>
Cc: Lorenzo Pieralisi <[e-mail]>
Signed-off-by: Ben Dooks <[e-mail]>
Signed-off-by: Sudeep Holla <[e-mail]>

arch/arm/plat-versatile/platsmp.c

···
 #include <asm/cacheflush.h>
 #include <asm/smp_plat.h>
 
+#include <plat/platsmp.h>
+
 /*
  * Write pen_release in a way that is guaranteed to be visible to all
  * observers, irrespective of whether they're taking part in coherency