Hardware: add SerialNumber support

Some manufacturers, e.g. Samsung and Acer, display a different
serial number in Settings -> About Phone than the one in
ro.serialno. This class enables the alternative serial number,
which is the one marked physically on the device, to be displayed.

Change-Id: If328ca7b487435b88246d1f8c47b04770183f09e
Merge branch 'cm-11.0' of https://github.com/CyanogenMod/android_frameworks_opt_hardware into temp