ASoC: davinci: fix DM365_EVM codec selection

An earlier bug fix of mine made the SND_DM365_VOICE_CODEC symbol
tristate to avoid creating an undefined reference from the
davinci-vcif.c driver to the davinci_soc_platform_register
function that may be in a module.

However, this may now lead to a different error on randconfig
kernels:

"warning: SND_DM365_VOICE_CODEC creates inconsistent choice state"

This happens because we now have a choice statement with
one bool and one tristate option, and the latter might not
support being set to 'y' because of dependencies.

This new change turns the other option into 'tristate' as well,
which avoids the problem.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Fixes: 19926c6d ("ASoC: davinci: vcif must be a module if SND_DAVINCI_SOC is")
Signed-off-by: Mark Brown <broonie@kernel.org>