First set of new device support, features and cleanups for IIO in the 4.5 cycle

Usual mixed bag, but the big item perhaps in this series is the DMA buffer
support added by Lars-Peter Clausen. It's been in the works for a long time
and it will be interesting to see what hardware support shows up now that
this is available.

New core features + associate cleanup.
* Add generic DMA buffer infrastructure
* Add a DMAengine framework based buffer
 Also associated minor changes.
   - Set the device buffer watermark based on the minimum watermark for all
     attached buffers rather than just the 'primary' one.
   - iio_buffer_init - only set the watermark default if one hasn't already
     been provided.  This allows simple support for devices with a fixed
     watermark.
   - read only attribute for watermark on fixed watermark devices.
   - add explicit buffer enable/disable callbacks to allow the buffer to
     do more than trivial actions when it is being turned on and off.
* IIO_VAL_INT support in write_raw_get_fmt function.

New device support
* Freescale MMA7455/7456L accelerometers
* Memsic MXC6255XC accelerometer
* ST lis2dh12 accelerometer
* TI ADS8688 ADC
* TI Palamas (twl6035/7) gpadc

New driver features
* mma8452
  - support either of the available interrupt pins to cope with the case
    where board layout has lead to a particular one being connected.

Staging graduation
* Dummy driver
  - this driver acts as both an example and a test device for those with
    out hardware to develop userspace code against.

Cleanups and minor bits and bobs.
* treewide
  - Sort out the ordering of iio_device_register/unregister vs runtime
    pm function calls so that it's all nice and consistent and not race
    prone.
  - Check sscanf return values.  None of the cases will actually happen as
    the strings are supplied internally, but best to be consistent on this.
* ad7780
  - switch over to the gpio descriptor interface and remove the now unused
    platform data which gets rid of a header entirely.
* ad7793
  - drop a pointless else statement.
* at91_adc
  - Swap kmalloc_array in for a kmalloc doing the same job.
* dummy
  - get rid of some commented out lines that snuck in during the move of
    the driver.
* lm3533-als
  - Print an error message on provision of an invalid resistance.
* mcp320x
  - Add compatible strings with vendor prefix and deprecate those with
    no vendor prefix.
* mxs-lradc
  - Use BIT macro in various places rather than shifted ones.
* pa12203001
  - Power off the chip if the registration fails.
* pulsedlight-lidar-lite
  - add runtime PM support.
* xilinx XADC
  - constify an iio_buffer_setup_ops structure.
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