x86/hevc: add 12bits support for deblocking filter

cherry picked from commit 97d46afe320c7d61d7b9525e5f5588355cde4bb0

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
x86/hevc: remove unused constant in deblocking filter

cherry picked from commit a3f7282eaa6f1ab0524fb966c6eade50c3025f99

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>