media: add configstore and check it for vpp enablement

Reduction in property usage. Go to the configstore to check whether vpp
should be enabled, instead of checking vendor.media.vpp.enable. If the
configstore is not enabled, fall back to the sysprop.

Expose the configstore through libplatformconfig, by adding static
methods to the Config class. Add a ConfigStore wrapper to allow C
implementations to access the ConfigStore.

Change-Id: Icb6b247b19f0adc107be636517d97b293229eb34
7 files changed