V4L/DVB (5813): TUNER_TEA5761 kconfig fixes

The following doesn't make much sense:
drivers/media/video/Kconfig:
...
config TUNER_TEA5761
        tristate "TEA 5761 radio tuner (EXPERIMENTAL)"
...
drivers/media/video/Makefile:
...
ifneq ($(CONFIG_TUNER_TEA5761),)
  tuner-objs += tea5761.o
endif
...
With this setup, TUNER_TEA5761=m is equivalent to TUNER_TEA5761=y.
This patch therefore changes TUNER_TEA5761 to a bool.
The missing dependency on EXPERIMENTAL the prompt text indicates also
gets added by this patch.
Additionally, the Makefile entry can now be written in a more compact way.

Signed-off-by: Adrian Bunk <bunk@stusta.de>
Signed-off-by: Michael Krufky <mkrufky@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>