Intersil ISL29034 ambient light sensor device driver for Google nanohub.

- Supported features:

A. Report ambient light data
B. Data rates: 10 Hz
C. I2C protocol

The device doesn't have an interrupt line, so a timer callback is used to
read the data.

- Platform/variant porting:

The driver requires that following macros are defined in the variant.h
file of the specific variant:

  ISL29034_I2C_BUS_ID    /* specify I2C Bus ID */
  ISL29034_I2C_SPEED     /* specify I2C Bus speed in Hz */

If these macros are not defined in the current variant the driver forces a
compile-time error.

An optional macro is available to specify the I2C address of ISL29034 device.
If the macro is not defined, the default value 0x44 would be used.

  ISL29034_I2C_ADDR      /* specify device I2C address */

An optional macro is available to enable debug information:

  ISL29034_DBG_ENABLED   /* Enable debug messages */

Example:

  /*
   * Define platform/variant dependent ISL29034 device macros
   */

  #define ISL29034_I2C_BUS_ID      0
  #define ISL29034_I2C_SPEED       400000
  #define ISL29034_I2C_ADDR        0x44