powerpc/msi: Fix compile error on mpc83xx

mpic_get_primary_version() is not defined when not using MPIC.
The compile error log like:

arch/powerpc/sysdev/built-in.o: In function `fsl_of_msi_probe':
fsl_msi.c:(.text+0x150c): undefined reference to `fsl_mpic_primary_get_version'
Signed-off-by: NJia Hongtao <hongtao.jia@freescale.com>
Signed-off-by: NScott Wood <scottwood@freescale.com>

arch/powerpc/include/asm/mpic.h

@@ -396,7 +396,14 @@ extern struct bus_type mpic_subsys;
 #define	MPIC_REGSET_TSI108		MPIC_REGSET(1)	/* Tsi108/109 PIC */
 
 /* Get the version of primary MPIC */
+#ifdef CONFIG_MPIC
 extern u32 fsl_mpic_primary_get_version(void);
+#else
+static inline u32 fsl_mpic_primary_get_version(void)
+{
+	return 0;
+}
+#endif
 
 /* Allocate the controller structure and setup the linux irq descs
  * for the range if interrupts passed in. No HW initialization is