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_SPIFLASH_defconfig b/configs/P2020RDB-PC_36BIT_SPIFLASH_defconfig
index e7c491a..73b43f7 100644
--- a/configs/P2020RDB-PC_36BIT_SPIFLASH_defconfig
+++ b/configs/P2020RDB-PC_36BIT_SPIFLASH_defconfig
@@ -5,6 +5,7 @@
 CONFIG_SPL_SPI_FLASH_SUPPORT=y
 CONFIG_SPL_SPI_SUPPORT=y
 CONFIG_MPC85xx=y
+# CONFIG_CMD_ERRATA is not set
 CONFIG_TARGET_P2020RDB=y
 CONFIG_PHYS_64BIT=y
 CONFIG_FIT=y