CHROMIUM: config: add LM90 driver on Exynos platforms

CHROMIUM: config: add LM90 driver on Exynos platforms

On Spring, we have a G781 thermal sensor on I2C bus 7.
The sensor is supported by the LM90 driver.

Signed-off-by: Vincent Palatin <vpalatin@chromium.org>
BUG=chrome-os-partner:16725
TEST=On spring, on the command-line
"cat /sys/bus/i2c/devices/7-004c/temp[12]_input"
and see board temperature in milli-celsius (e.g. 50750)

Change-Id: I561df7bdc85cc07221235e85212a42b26598f5a4
Reviewed-on: https://gerrit.chromium.org/gerrit/42335
Commit-Queue: Vincent Palatin <vpalatin@chromium.org>
Tested-by: Vincent Palatin <vpalatin@chromium.org>
Reviewed-by: Vincent Palatin <vpalatin@chromium.org>