dcmi: implement get sensor info

This commit implements the plumbing around the 'Get Sensor
Info' command. It doesn't read the sensor information yet.
That code is coming up in a subsequent commit.

Refactor some of the get temperature readings code, in order to reuse
certain common aspects for this commit.

Change-Id: I0cb531b5b75e98cc9e76509f84f832be9997fee0
Signed-off-by: Deepak Kodihalli <dkodihal@in.ibm.com>
3 files changed