cameraHAL: enable HWA; detect & use correct libgralloc version

Change-Id: If9573fbdf77f31116ec76a05da5250e11a13653e
galaxy5: enable purgeable assets by default

The galaxy5 only has 256MB RAM (181MB usable to userspace)

Change-Id: I8e5453150d1299fa0d98580c7864d5d0ff9d65ff