[media] staging: add MEDIA_SUPPORT dependency

staging media drivers tend to have a build time dependency on the
media support. In particular, the newly added pulse8 cec driver can
only be a loadable module if MEDIA_SUPPORT=m, but its build dependency
is on a 'bool' symbol (MEDIA_CEC), so a randconfig build can fail
with pulse8_cec built-in:

drivers/staging/built-in.o: In function `pulse8_disconnect':
dgnc_utils.c:(.text+0x114): undefined reference to `cec_unregister_adapter'
drivers/staging/built-in.o: In function `pulse8_irq_work_handler':
dgnc_utils.c:(.text+0x1bc): undefined reference to `cec_transmit_done'
dgnc_utils.c:(.text+0x1d8): undefined reference to `cec_received_msg'
dgnc_utils.c:(.text+0x1f4): undefined reference to `cec_transmit_done'
dgnc_utils.c:(.text+0x218): undefined reference to `cec_transmit_done'
dgnc_utils.c:(.text+0x23c): undefined reference to `cec_transmit_done'
drivers/staging/built-in.o: In function `pulse8_connect':
dgnc_utils.c:(.text+0x844): undefined reference to `cec_allocate_adapter'
dgnc_utils.c:(.text+0x8a4): undefined reference to `cec_delete_adapter'
dgnc_utils.c:(.text+0xa10): undefined reference to `cec_register_adapter'

Originally, MEDIA_CEC itself was a tristate symbol, which would have
prevented this, but since 5bb2399a ("[media] cec: fix Kconfig
dependency problems"), it doesn't work like that any more.

This encloses all of the staging media drivers in a CONFIG_MEDIA_SUPPORT
dependency in Kconfig, which solves the problem by enforcing that none
of the drivers can be built-in if the media core is a module.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>