topology: Merge an element's be & cc pointer to one link pointer

topology: Merge an element's be & cc pointer to one link pointer

Code refactoring. Previously an element has two pointers, 'be' and 'cc',
for BE (Back End) and CC (Codec-Codec) link respectively. But actually
the topology tool processes BE and CC links in the same way, so these
two pointers can be merged into one 'link' pointer, which can be used
configure any physical links.

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