[media] staging: media: davinci_vfpe: allow modular build

It has never been possible to actually build this driver as
a loadable module, only built-in because the Makefile attempts
to build each file into its own module and fails:

ERROR: "mbus_to_pix" [drivers/staging/media/davinci_vpfe/vpfe_video.ko] undefined!
ERROR: "vpfe_resizer_register_entities" [drivers/staging/media/davinci_vpfe/vpfe_mc_capture.ko] undefined!
ERROR: "rsz_enable" [drivers/staging/media/davinci_vpfe/dm365_resizer.ko] undefined!
ERROR: "config_ipipe_hw" [drivers/staging/media/davinci_vpfe/dm365_ipipe.ko] undefined!
ERROR: "ipipe_set_lutdpc_regs" [drivers/staging/media/davinci_vpfe/dm365_ipipe.ko] undefined!

It took a long time to catch this bug with randconfig builds
because at least 14 other Kconfig symbols have to be enabled in
order to configure this one, and it was clearly only ever tested
as built-in with mainline kernels, if at all.

The solution is really easy: this patch changes the Makefile to
link all files into one module. As discussed previously, the
driver has never before used successfully as a loadable module,
but there is no reason to prevent that configuration.

Link: http://lkml.iu.edu/hypermail/linux/kernel/1512.1/02383.html



Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>