powerpc/mpc85xx: Make NMG_CPU_A011 workaround conditional

This erratum applies to the following SoCs:
P4080 rev 1.0, 2.0, fixed in rev 3.0
P2041 rev 1.0, 1.1, fixed in rev 2.0
P3041 rev 1.0, 1.1, fixed in rev 2.0.

Workaround for erratum NMG_CPU_A011 is enabled by default. This workaround
may degrade performance. P4080 erratum CPU22 shares the same workaround.
So it is always enabled for P4080. For other SoCs, it can be disabled by
hwconfig with syntax:

fsl_cpu_a011:disable

Signed-off-by: York Sun <yorksun@freescale.com>
Signed-off-by: Andy Fleming <afleming@freescale.com>
diff --git a/arch/powerpc/cpu/mpc85xx/cmd_errata.c b/arch/powerpc/cpu/mpc85xx/cmd_errata.c
index 4e1a54a..858b3f8 100644
--- a/arch/powerpc/cpu/mpc85xx/cmd_errata.c
+++ b/arch/powerpc/cpu/mpc85xx/cmd_errata.c
@@ -27,6 +27,9 @@
 
 static int do_errata(cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[])
 {
+#ifdef CONFIG_SYS_FSL_ERRATUM_NMG_CPU_A011
+	extern int enable_cpu_a011_workaround;
+#endif
 	__maybe_unused u32 svr = get_svr();
 
 #if defined(CONFIG_FSL_SATA_V2) && defined(CONFIG_FSL_SATA_ERRATUM_A001)
@@ -56,8 +59,9 @@
 	/*
 	 * NMG_CPU_A011 applies to P4080 rev 1.0, 2.0, fixed in 3.0
 	 * also applies to P3041 rev 1.0, 1.1, P2041 rev 1.0, 1.1
+	 * The SVR has been checked by cpu_init_r().
 	 */
-	if (SVR_SOC_VER(svr) != SVR_P4080 || SVR_MAJ(svr) < 3)
+	if (enable_cpu_a011_workaround)
 		puts("Work-around for Erratum CPU-A011 enabled\n");
 #endif
 #if defined(CONFIG_SYS_FSL_ERRATUM_CPU_A003999)