ASoC: rt5651: move definitions of dt-binding constants to include/dt-bindings

Move the definitions of constants used in the dt-bindings from
include/sound/rt5651.h to include/dt-bindings/sound/rt5651.h.

As dt-bindings headers may also be parsed by the dt-compiler, they cannot
use enums, only defines, so this commit also changes the code declaring
the constants to use defines.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Mark Brown <broonie@kernel.org>