Sysconfig: Allow runtime differentiation of product configuration

Single product partition can support multiple sku's with different
capabilities.
Add support to load configuration xml's from below locations.

product/etc/sysconf/sku_${ro.boot.hardware.sku}/*.xml
product/etc/permissions/sku_${ro.boot.hardware.sku}/*.xml

Fixes: 149416322
Bug: 149416322
Test: Manual, copy configuration file to above locations, confirm
      in logcat that files are loaded.
Change-Id: Ia945fb105403256ec335859579df51bad6c9860a