Convert CONFIG_CMD_ESBC_VALIDATE to Kconfig

This converts the following to Kconfig:
   CONFIG_CMD_ESBC_VALIDATE

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Tom Rini <trini@konsulko.com>
diff --git a/board/freescale/common/Kconfig b/board/freescale/common/Kconfig
index 5408857..b4bf90d 100644
--- a/board/freescale/common/Kconfig
+++ b/board/freescale/common/Kconfig
@@ -7,3 +7,12 @@
 	select SHA_PROG_HW_ACCEL
 	bool
 	default y
+
+config CMD_ESBC_VALIDATE
+	bool "Enable the 'esbc_validate' and 'esbc_halt' commands"
+	default y if CHAIN_OF_TRUST
+	help
+	  This option enables two commands used for secure booting:
+
+	    esbc_validate - validate signature using RSA verification
+	    esbc_halt - put the core in spin loop (Secure Boot Only)