avutil: Add a copy of ff_sqrt_tab back into avutil to restore ABI compatibility

avutil: Add a copy of ff_sqrt_tab back into avutil to restore ABI compatibility

Earlier versions of for instance of libavcodec expect this symbol to be
present in libavutil. This commit can be reverted after the next major
bump.

New shared builds of avcodec will link to the internal copy of the
table within that library, so those builds won't rely on this table
being present in avutil any longer either.

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