topology: Parse vendor private data for manifest

topology: Parse vendor private data for manifest

In text conf file, user can define a manifest section and let it refer
to private data sections, in the same syntax as other element types.

The text conf file can have at most 1 manifest section.

Signed-off-by: Mengdong Lin <mengdong.lin@linux.intel.com>
Reviewed-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>