enhancement: more neon accerleration for vc-1

[spotter]

Summary of the bug:

comparing x86 optimizations to arm, it seems there are a number of optimizations that exist in the x86 space that don't exist for arm.

I've noticed this on my Sony Android TV which seems to be defective in that even though it has support for VC-1, it's not exporting that support via mediacodecs.

see: ​https://github.com/CiNcH83/bravia_atv2/issues/4 (and even their built in player is buggy with it see ​https://github.com/CiNcH83/bravia_atv2/issues/76)

so decided to explore what could be done to optimize vc-1 software rendering.

I cam across the samsung paper that shows major improvements: ​http://www.ncc.org.in/download.php?f=NCC2010/B2_3.pdf (in digging into the asm hooks that ffmpeg's video decoder has, I'm guessing this paper isn't new to ffmpeg's developers)

and then dug into ffmpeg where I saw that it seems that there a lot more x86 hooks that do't exist for arm (example loopfilter). I'm wondering if this is a conscious decision? (i.e. because of limitations of neon it can't be done effectively) or an oversight and in truth arm should have an equivalent set of vector instructions like x86?