Build ODM manifests and fragments for each SKU.

In BoardConfig.mk, ODM manifests can be specify as follows:

    # installed to /odm/etc/vintf/manifest.xml
    ODM_MANIFEST_FILES := device/foo/bar/odm_manifest.xml

    # installed to /odm/etc/vintf/manifest_baz.xml
    ODM_MANIFEST_SKUS := baz
    ODM_MANIFEST_BAZ_FILES := device/foo/bar/odm_manifest_baz.xml

This is preferred over PRODUCT_COPY_FILES because it uses
assemble_vintf to check manifest at build time.

Test: builds

Change-Id: I18517b8ba09d3271627d6f21b8250b1bfc9e5db3