powerpc: Fix P10 PVR revision in /proc/cpuinfo for SMT4 cores

On POWER10 bit 12 in the PVR indicates if the core is SMT4 or SMT8.
Bit 12 is set for SMT4.

Without this patch, /proc/cpuinfo on a SMT4 DD1 POWER10 looks like
this:
  cpu             : POWER10, altivec supported
  revision        : 17.0 (pvr 0080 1100)

Fixes: a3ea40d5 ("powerpc: Add POWER10 architected mode")
Cc: stable@vger.kernel.org # v5.8
Signed-off-by: Michael Neuling <mikey@neuling.org>
Reviewed-by: Vaidyanathan Srinivasan <svaidy@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200803035600.1820371-1-mikey@neuling.org

arch/powerpc/kernel/setup-common.c

@@ -311,6 +311,7 @@ static int show_cpuinfo(struct seq_file *m, void *v)
 				min = pvr & 0xFF;
 				break;
 			case 0x004e: /* POWER9 bits 12-15 give chip type */
+			case 0x0080: /* POWER10 bit 12 gives SMT8/4 */
 				maj = (pvr >> 8) & 0x0F;
 				min = pvr & 0xFF;
 				break;