Make relative path for native_bridge binaries configurable

This change introduces NativeBridgeRelativePath and
NativeBridgeSecondaryRelativePath product variables to
make relative path to native_bridge binaries configurable.

It also removes moves information about native bridge
host architecture to Target and sets it during decodeTargetProductVariables

Test: make PRODUCT-cf_x86_phone-userdebug dist
Change-Id: Ie736e81eae507e1775566ce9f29135011b12af27