apphandler: Add storage for Get/Set System Info Parameter

All but one standard System Info Parameter and most (all?) OEM
parameters are string type. Add a interface to connect string callbacks
to System Info Parameter selector codes. Also add a convenience call
that can connect a static string to a parameter selector code.

Change-Id: I5e35d0418b8ddf5b2575fac093acfc7d7ca2217c
Signed-off-by: Xo Wang <xow@google.com>
Signed-off-by: Patrick Venture <venture@google.com>
3 files changed