yuv constants for bt.601 were previously ported to neon64, as well
as the code to respect other color spaces.  But the jpeg and bt.709
colour conversion constants were still in armv7 form.  This changes
the constants for aarch64 builds to be compatible with the code.

yuv constants are now passed as const *

Remove Yvu constants which were used for older version on nv21 but not new code.

TBR=harryjin@google.com
BUG=none

Review URL: https://codereview.chromium.org/1398623002 .