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/cpu/mpc8xx/cpu.c b/arch/powerpc/cpu/mpc8xx/cpu.c
index 9da73ac..5a81bed 100644
--- a/arch/powerpc/cpu/mpc8xx/cpu.c
+++ b/arch/powerpc/cpu/mpc8xx/cpu.c
@@ -42,7 +42,7 @@
 
 	/* the highest 16 bits should be 0x0050 for a 860 */
 
-	if ((pvr >> 16) != 0x0050)
+	if (PVR_VER(pvr) != PVR_VER(PVR_8xx))
 		return -1;
 
 	k = (immr << 16) |