topology: Define new type and section name to configure physical links

topology: Define new type and section name to configure physical links

Users may not use DPCM but still need to configure the physical links.
So we should not only consider backend links for DPCM.

- SND_TPLG_TYPE_LINK is defined to configure physical links by C API.
  And SND_TPLG_TYPE_BE is still supported to configure Backend links for
  DPCM cases.

- SectionLink can be used to configure physical links in text conf file.
  And SectionBE is still supported to config Backend links for DPCM cases.

Actually, users can use SND_TPLG_TYPE_LINK and SectionLink to configure
backend links for DPCM cases, because BE links are also physical links.
The parsing is same and we rename the function from tplg_parse_be to
tplg_parse_link.

Signed-off-by: Mengdong Lin <mengdong.lin@linux.intel.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>