V4L/DVB: tm6000: fix build errors

V4L/DVB: tm6000: fix build errors

(1) tm6000 uses usb_*() interfaces, so it should depend on USB.

drivers/built-in.o: In function `tm6000_usb_disconnect':
tm6000-cards.c:(.text+0x4abb44): undefined reference to `usb_put_dev'
drivers/built-in.o: In function `tm6000_usb_probe':
tm6000-cards.c:(.text+0x4ac923): undefined reference to `usb_get_dev'
tm6000-cards.c:(.text+0x4ac93c): undefined reference to `usb_set_interface'
drivers/built-in.o: In function `tm6000_read_write_usb':
(.text+0x4ad274): undefined reference to `usb_control_msg'
drivers/built-in.o: In function `tm6000_uninit_isoc':
tm6000-video.c:(.text+0x4b00d5): undefined reference to `usb_kill_urb'
tm6000-video.c:(.text+0x4b00e4): undefined reference to `usb_unlink_urb'
tm6000-video.c:(.text+0x4b013c): undefined reference to `usb_buffer_free'
tm6000-video.c:(.text+0x4b014b): undefined reference to `usb_free_urb'
drivers/built-in.o: In function `tm6000_prepare_isoc':
tm6000-video.c:(.text+0x4b0773): undefined reference to `usb_alloc_urb'
tm6000-video.c:(.text+0x4b0835): undefined reference to `usb_buffer_alloc'
drivers/built-in.o: In function `tm6000_irq_callback':
tm6000-video.c:(.text+0x4b1ad3): undefined reference to `usb_submit_urb'
drivers/built-in.o: In function `tm6000_module_init':
tm6000-cards.c:(.init.text+0x24499): undefined reference to `usb_register_driver'
drivers/built-in.o: In function `tm6000_module_exit':
tm6000-cards.c:(.exit.text+0x5cb0): undefined reference to `usb_deregister'

(2) tm6000-alsa uses interfaces from tm6000-core, so when they are
both built as modules, the core interfaces need to be exported.

ERROR: "tm6000_set_reg" [drivers/staging/tm6000/tm6000-alsa.ko] undefined!
ERROR: "tm6000_get_reg" [drivers/staging/tm6000/tm6000-alsa.ko] undefined!

Cc: linux-next@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>, 	linux-media@vger.kernel.org
Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Cc: Mauro Carvalho Chehab <mchehab@infradead.org>
Cc: Michel Ludwig <michel.ludwig@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>