framebuffer: don't link fb_devio into kernel image unconditionally

CONFIG_FB_DEFERRED_IO is defined as bool while CONFIG_FB is defined as
tristate. Currently fb_defio.o is linked into the kernel image even if
CONFIG_FB=m.

I fix this by updating the Makefile to link fb_defio.o into fb.o and thus
go into one place with the other core framebuffer code.

Signed-off-by: Harald Geyer <[e-mail]>
Signed-off-by: Tomi Valkeinen <[e-mail]>

drivers/video/fbdev/core/Makefile

···
 obj-$(CONFIG_FB)                  += fb.o
 fb-y                              := fbmem.o fbmon.o fbcmap.o fbsysfs.o \
                                      modedb.o fbcvt.o
+fb-$(CONFIG_FB_DEFERRED_IO)       += fb_defio.o
 fb-objs                           := $(fb-y)
 
 obj-$(CONFIG_FB_CFB_FILLRECT)  += cfbfillrect.o
···
 obj-$(CONFIG_FB_SYS_FOPS)      += fb_sys_fops.o
 obj-$(CONFIG_FB_SVGALIB)       += svgalib.o
 obj-$(CONFIG_FB_DDC)           += fb_ddc.o
-obj-$(CONFIG_FB_DEFERRED_IO)   += fb_defio.o

drivers/video/fbdev/core/fb_defio.c

···
 	mutex_destroy(&fbdefio->lock);
 }
 EXPORT_SYMBOL_GPL(fb_deferred_io_cleanup);
-
-MODULE_LICENSE("GPL");