Add support for Semtech SX150-series I2C GPIO expanders.  Compatible
models include:

8 bits:  sx1508q
16 bits: sx1509q
Signed-off-by: NGregory Bean <gbean@codeaurora.org>
Cc: David Brownell <david-b@pacbell.net>
Cc: Jean Delvare <khali@linux-fr.org>
Cc: Trilok Soni <tsoni@codeaurora.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>