avfilter: Add missing emms_c when needed

Arch specific calls should have an emms_c following to keep the cpu
state consistent.

Reported-By: wm4
CC: libav-stable@libav.org
(cherry picked from commit e995cf1bccc6e91bbaa6a8771e23fb3ab259c110)
arm: hpeldsp: prevent overreads in armv6 asm

Based on a patch by Russel King <rmk+libav@arm.linux.org.uk>

Bug-Id: 646
CC: libav-stable@libav.org
(cherry picked from commit cbddee1cca0ebd01e8c5aa694d31228eb4de4b41)
arm: hpeldsp: fix put_pixels8_y2_{,no_rnd_}armv6

The overread avoidance fix in cbddee1cca0ebd01e8c5aa694d31228eb4de4b41
broke the computation for the last row since it prevented the safe
reading from the height+1-th row.

CC: libav-stable@libav.org
(cherry picked from commit 61985ad72c47bbb668f2d3923bf5c9df83e79323)
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