Add support for ROHM BH1780GLI Ambient light sensor.

BH1780 supports I2C interface.  Driver supports read/update of power state
and read of lux value (through SYSFS).  Writing value 3 to power_state
enables the sensor and current lux value could be read.

Currently this driver follows the same sysfs convention as supported by
drivers/misc/isl29003.c.
Signed-off-by: Hemanth V <hemanthv@ti.com>
Reviewed-by: Daniel Mack <daniel@caiaq.de>
Acked-by: Jonathan Cameron <jic23@cam.ac.uk>
Cc: Jean Delvare <khali@linux-fr.org>
Cc: Wolfram Sang <w.sang@pengutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>