powerpc: mpc8xx: get rid of the multiple PVR_ values

Avoid hardcoding the PVR values in C since they are defined
in processor.h

At the same time, remove those multiple PVR values for 8xx and
keep only one that we call PVR_8xx

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
diff --git a/arch/powerpc/include/asm/processor.h b/arch/powerpc/include/asm/processor.h
index 57b11b8..6fbe8c4 100644
--- a/arch/powerpc/include/asm/processor.h
+++ b/arch/powerpc/include/asm/processor.h
@@ -973,10 +973,8 @@
  * differentiated by the version number in the Communication Processor
  * Module (CPM).
  */
-#define PVR_821		0x00500000
-#define PVR_823		PVR_821
-#define PVR_850		PVR_821
-#define PVR_860		PVR_821
+#define PVR_8xx		0x00500000
+
 #define PVR_7400	0x000C0000
 
 /*