mmc: add bkops-enable command

Add new command that provides possibility to enable the
background operations handshake functionality
(BKOPS_EN, EXT_CSD byte [163]) on eMMC devices.

This is an optional feature of eMMCs, the setting is write-once.
The command must be explicitly taken into use with
CONFIG_CMD_BKOPS_ENABLE.

Signed-off-by: Tomas Melin <tomas.melin@vaisala.com>
diff --git a/cmd/Kconfig b/cmd/Kconfig
index b16c603..7653c60 100644
--- a/cmd/Kconfig
+++ b/cmd/Kconfig
@@ -572,6 +572,15 @@
 	help
 	  Show AMBA Plug-n-Play information on startup.
 
+config CMD_BKOPS_ENABLE
+	bool "mmc bkops enable"
+	depends on CMD_MMC
+	default n
+	help
+	  Enable command for setting manual background operations handshake
+	  on a eMMC device. The feature is optionally available on eMMC devices
+	  conforming to standard >= 4.41.
+
 config CMD_BLOCK_CACHE
 	bool "blkcache - control and stats for block cache"
 	depends on BLOCK_CACHE