HID: Use Kbuild idiom in Makefiles

Use <driver>-$(CONFIG_FOO) syntax to build multipart objects with
optional parts, since all the config options are bool. Also, delete the
obvious comments in the usbhid Makefile.

Signed-off-by: Michal Marek <mmarek@suse.cz>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
diff --git a/drivers/hid/usbhid/Makefile b/drivers/hid/usbhid/Makefile
index db3cf31..890f291 100644
--- a/drivers/hid/usbhid/Makefile
+++ b/drivers/hid/usbhid/Makefile
@@ -2,17 +2,9 @@
 # Makefile for the USB input drivers
 #
 
-# Multipart objects.
 usbhid-y	:= hid-core.o hid-quirks.o
-
-# Optional parts of multipart objects.
-
-ifeq ($(CONFIG_USB_HIDDEV),y)
-	usbhid-y	+= hiddev.o
-endif
-ifeq ($(CONFIG_HID_PID),y)
-	usbhid-y	+= hid-pidff.o
-endif
+usbhid-$(CONFIG_USB_HIDDEV)	+= hiddev.o
+usbhid-$(CONFIG_HID_PID)	+= hid-pidff.o
 
 obj-$(CONFIG_USB_HID)		+= usbhid.o
 obj-$(CONFIG_USB_KBD)		+= usbkbd.o