aarch64: vp8: Port epel4 functions from arm version

aarch64: vp8: Port epel4 functions from arm version

                      Cortex A53    A72    A73
vp8_put_epel4_h4_c:        631.4  291.7  367.8
vp8_put_epel4_h4_neon:     241.0  131.0  155.7
vp8_put_epel4_h4v4_c:      967.5  529.3  667.7
vp8_put_epel4_h4v4_neon:   429.3  241.8  279.7
vp8_put_epel4_h4v6_c:     1374.7  657.5  864.5
vp8_put_epel4_h4v6_neon:   515.5  295.5  334.7
vp8_put_epel4_h6_c:        851.0  421.0  486.0
vp8_put_epel4_h6_neon:     321.5  195.0  217.7
vp8_put_epel4_h6v4_c:     1111.3  621.1  781.2
vp8_put_epel4_h6v4_neon:   539.2  328.0  365.3
vp8_put_epel4_h6v6_c:     1561.3  763.3  999.7
vp8_put_epel4_h6v6_neon:   645.5  401.0  434.7
vp8_put_epel4_v4_c:        663.8  298.3  357.0
vp8_put_epel4_v4_neon:     116.0   81.5   72.5
vp8_put_epel4_v6_c:        870.5  437.0  507.4
vp8_put_epel4_v6_neon:     147.7  108.8   92.0

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