drivers: console: fix cmake empty library warning

When there is no console driver enabled, cmake warns that
the library has no sources. So only include the console
directory when CONFIG_CONSOLE is enabled.

Signed-off-by: Daniel Leung <daniel.leung@intel.com>
diff --git a/drivers/CMakeLists.txt b/drivers/CMakeLists.txt
index ff47275..3458c9a 100644
--- a/drivers/CMakeLists.txt
+++ b/drivers/CMakeLists.txt
@@ -2,7 +2,6 @@
 
 add_definitions(-D__ZEPHYR_SUPERVISOR__)
 
-add_subdirectory(console)
 add_subdirectory(interrupt_controller)
 add_subdirectory(misc)
 add_subdirectory(pcie)
@@ -12,6 +11,7 @@
 add_subdirectory_ifdef(CONFIG_ADC adc)
 add_subdirectory_ifdef(CONFIG_CLOCK_CONTROL clock_control)
 add_subdirectory_ifdef(CONFIG_COUNTER counter)
+add_subdirectory_ifdef(CONFIG_CONSOLE console)
 add_subdirectory_ifdef(CONFIG_CRYPTO crypto)
 add_subdirectory_ifdef(CONFIG_DAC dac)
 add_subdirectory_ifdef(CONFIG_DISPLAY display)