powerpc: Added __cmpdi2 for signed 64bit comparision

This was missing on powerpc and I am getting compilation error
drivers/vfio/pci/vfio_pci_rdwr.c:193: undefined reference to `__cmpdi2'
drivers/vfio/pci/vfio_pci_rdwr.c:193: undefined reference to `__cmpdi2'

Signed-off-by: Bharat Bhushan <[e-mail]>
Signed-off-by: Benjamin Herrenschmidt <[e-mail]>

arch/powerpc/kernel/misc_32.S

···
 	blr
 
 /*
+ * 64-bit comparison: __cmpdi2(s64 a, s64 b)
+ * Returns 0 if a < b, 1 if a == b, 2 if a > b.
+ */
+_GLOBAL(__cmpdi2)
+	cmpw	r3,r5
+	li	r3,1
+	bne	1f
+	cmplw	r4,r6
+	beqlr
+1:	li	r3,0
+	bltlr
+	li	r3,2
+	blr
+/*
  * 64-bit comparison: __ucmpdi2(u64 a, u64 b)
  * Returns 0 if a < b, 1 if a == b, 2 if a > b.
  */

arch/powerpc/kernel/ppc_ksyms.c

···
 EXPORT_SYMBOL(__lshrdi3);
 int __ucmpdi2(unsigned long long, unsigned long long);
 EXPORT_SYMBOL(__ucmpdi2);
+int __cmpdi2(long long, long long);
+EXPORT_SYMBOL(__cmpdi2);
 #endif
 long long __bswapdi2(long long);
 EXPORT_SYMBOL(__bswapdi2);