Refactors all of the DAC drivers to use a shared driver class
initialization priority configuration, CONFIG_DAC_INIT_PRIORITY, to
allow configuring DAC drivers separately from other devices. This is
similar to other driver classes like I2C and SPI.
The default is set to CONFIG_KERNEL_INIT_PRIORITY_DEVICE to preserve the
existing default initialization priority for most drivers. The
exceptions are dacx0508, dacx3608, and mcp4725 drivers which have
dependencies on SPI or I2C drivers and must therefore initialize later
than the default device priority.
Signed-off-by: Maureen Helm <maureen.helm@intel.com>
