Convert CONFIG_CMD_ERRATA to Kconfig

This converts the following to Kconfig:
   CONFIG_CMD_ERRATA

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/P2020RDB-PC_36BIT_defconfig b/configs/P2020RDB-PC_36BIT_defconfig
index 4de5745..4cc77fa 100644
--- a/configs/P2020RDB-PC_36BIT_defconfig
+++ b/configs/P2020RDB-PC_36BIT_defconfig
@@ -1,5 +1,6 @@
 CONFIG_PPC=y
 CONFIG_MPC85xx=y
+# CONFIG_CMD_ERRATA is not set
 CONFIG_TARGET_P2020RDB=y
 CONFIG_PHYS_64BIT=y
 CONFIG_FIT=y