dcmi : implement get temperature readings

This commit implements the plumbing around the 'Get Temperature
Readings' command. It doesn't read the temperatures from the relevant
sensors. That code is coming up in a subsequent commit.

Change-Id: I4514b65eb3ca65d52dd35185338a2c397e9a76ca
Signed-off-by: Deepak Kodihalli <dkodihal@in.ibm.com>
3 files changed