add support for overriding build.prop settings.

Change-Id: Ie4224d608b7bcb0c2087bd77bc954f8f5f9b6495
Add ARMv6J and ARMv6-VFP processor combo option

Cherry-picked from gingerbread branch.

Change-Id: I8015149184ab3e1ee61ef93c62a395233ad1d156