drivers: misc: ti_dac7512: Remove duplicate driver

drivers: misc: ti_dac7512: Remove duplicate driver

The Texas Instruments DAC7512 has the exact same pinout, programming
interface and power-down modes as the Texas Instruments DAC121S101 and
Analog Devices AD5320, which are already supported by the IIO driver
ad5446.c.  Remove the duplicate misc driver.

This requires user space to migrate to the standardized IIO sysfs ABI.
(In other words, it needs to change a filename.)

The IIO driver supports the chip's features more fully, e.g. the ability
to power down the output or choose one of the available powerdown modes.

There is an oddity with the misc driver in that it initializes the SPI
slave to SPI_MODE_0, in contradiction to the datasheet which specifies
that data is latched in on the falling edge, implying that SPI_MODE_1
or SPI_MODE_2 must be used.  Another oddity is that Kconfig and the
MODULE_DESCRIPTION() claim the chip has 16-bit resolution although it
actually has 12-bit.

Datasheets:
http://www.ti.com/lit/ds/symlink/dac7512.pdf
http://www.ti.com/lit/ds/symlink/dac121s101.pdf
http://www.analog.com/media/en/technical-documentation/data-sheets/AD5320.pdf

Signed-off-by: Lukas Wunner <lukas@wunner.de>
Acked-by: Daniel Mack <daniel@zonque.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>