msm: socinfo: Introduce soc string

SOC vendors require the soc-id to be translated to a string
by the kernel and reported as a part of machine init
routines. Add support for it.

Change-Id: I8a0c13b235ebbe49b604c878ecb9a4874bc62307
Signed-off-by: Abhimanyu Kapur <abhimany@codeaurora.org>