kbuild: Allow to specify composite modules with modname-m

This allows to write

  drm-$(CONFIG_AGP) += drm_agpsupport.o

without having to handle CONFIG_AGP=y vs. CONFIG_AGP=m. Only support
this syntax for modules, since built-in code depending on something
modular cannot work and init/Makefile actually relies on the current
semantics. There are a few drivers which adapted to the current
semantics out of necessity; these are fixed to also work when the
respective subsystem is modular.

Acked-by: Peter Chen <peter.chen@freescale.com> [chipidea]
Signed-off-by: Michal Marek <mmarek@suse.com>
diff --git a/drivers/usb/chipidea/otg_fsm.h b/drivers/usb/chipidea/otg_fsm.h
index 2689375..262d6ef 100644
--- a/drivers/usb/chipidea/otg_fsm.h
+++ b/drivers/usb/chipidea/otg_fsm.h
@@ -62,7 +62,7 @@
 /* SSEND time before SRP */
 #define TB_SSEND_SRP         (1500)	/* minimum 1.5 sec, section:5.1.2 */
 
-#ifdef CONFIG_USB_OTG_FSM
+#if IS_ENABLED(CONFIG_USB_OTG_FSM)
 
 int ci_hdrc_otg_fsm_init(struct ci_hdrc *ci);
 int ci_otg_fsm_work(struct ci_hdrc *ci);