drivers: sensor: tmp116: Add support for SENSOR_ATTR_OFFSET.

TMP117 from TI is a sensor similar to tmp116, but it has more precision
and it also supports the offset register.
Add support for SENSOR_ATTR_OFFSET, which is used by TMP117 to the
pre-exisiting tmp116 driver.

This commit also enables multiple instances and adds TMP117 to Kconfig.

Signed-off-by: Puranjay Mohan <puranjay12@gmail.com>