[media] cx88: fix build when VP3054=m and CX88_DVB=y

[media] cx88: fix build when VP3054=m and CX88_DVB=y

As reported by Jim Davis <jim.epost@gmail.com>:

randconfig build error with next-20130813, in drivers/media/pci/cx88,
when:
	CONFIG_VIDEO_CX88=y
	CONFIG_VIDEO_CX88_BLACKBIRD=m
	CONFIG_VIDEO_CX88_DVB=y
	CONFIG_VIDEO_CX88_VP3054=m
	CONFIG_VIDEO_CX88_MPEG=y

  LD      init/built-in.o
drivers/built-in.o: In function `cx8802_dvb_remove':
cx88-dvb.c:(.text+0x3a9914): undefined reference to `vp3054_i2c_remove'
drivers/built-in.o: In function `cx8802_dvb_probe':
cx88-dvb.c:(.text+0x3a9c4b): undefined reference to `vp3054_i2c_probe'
make: *** [vmlinux] Error 1

That happens because the vp3054 symbols aren't available builtin.
So, make it builtin, if CX88_DVB=y, or module otherwise, if this
support is selected.

Reported-by: Jim Davis <jim.epost@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>