cmd: license: Add CONFIG_GZIP dependency

'License' command processing code could be successfully compiled only
when CONFIG_GZIP option is enabled, otherwise it can't find the 'gunzip'
function definition (it is defined in lib/gunzip.c).

Add CONFIG_GZIP dependency to 'license' command config option in the
corresponding Kconfig.

Signed-off-by: Ivan Orlov <ivan.orlov@codethink.co.uk>
diff --git a/cmd/Kconfig b/cmd/Kconfig
index 46600e5..50625e7 100644
--- a/cmd/Kconfig
+++ b/cmd/Kconfig
@@ -192,6 +192,7 @@
 config CMD_LICENSE
 	bool "license"
 	select BUILD_BIN2C
+	depends on GZIP
 	help
 	  Print GPL license text