configure: Add a dependency on vc1_decoder from vc1_parser

This fixes builds with vc1_parser enabled without vc1_decoder. All
the vc1_decoder object files were included in the vc1_parser line
in libavcodec/Makefile before, but architecture specific object files
for vc1_decoder were not.

Signed-off-by: Martin Storsjö <martin@martin.st>