drivers: hwinfo: fix shell dependency

The hwinfo shell uses shell functions and thus doesn't build when
CONFIG_SHELL=n. Fix that by adding a dependency on SHELL.

Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
diff --git a/drivers/hwinfo/Kconfig b/drivers/hwinfo/Kconfig
index 2881756..df2c7ec 100644
--- a/drivers/hwinfo/Kconfig
+++ b/drivers/hwinfo/Kconfig
@@ -15,6 +15,7 @@
 
 config HWINFO_SHELL
 	bool "Enable HWINFO Shell"
+	depends on SHELL
 	help
 	  Enable hwinfo Shell for testing.