Kconfig: Convert CMD_READ to Kconfig

Convert this option and enable it in sandbox. Also correct a bug which
was introduced with the block-device driver model conversion.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
diff --git a/cmd/Kconfig b/cmd/Kconfig
index ef614a6..0d9292b 100644
--- a/cmd/Kconfig
+++ b/cmd/Kconfig
@@ -749,6 +749,11 @@
 	  about 1990. These devices are typically removable memory or network
 	  cards using a standard 68-pin connector.
 
+config CMD_READ
+	bool "read - Read binary data from a partition"
+	help
+	  Provides low-level access to the data in a partition.
+
 config CMD_REMOTEPROC
 	bool "remoteproc"
 	depends on REMOTEPROC