Use the decoder versions of the functions (which are capable
of handling widths 4/8/16 for luma, not only 16 as in the
encoder). By using the more generic versions, there may be a small
performance loss since the functions need to check the width
in every call. Actual measurements show that the actual change is
very small (and the shared routines turn out to actually be faster
than the existing ones in ARM NEON setups).
Even if there actually is no SIMD optimized version of the
width==2 cases, luma function for SIMD still needs to handle
it by calling McCopyWidthEq2_c for these cases.
This simplifies the UT code a little, and makes sure that
those codepaths are tested properly.
This speeds up the compile time from 21.3 to 2.6 seconds
for the MC test files.
This makes it slightly harder to see exactly which test
failed on a quick glance, but it makes the overall structure of
the unit test output more manageable and readable, by reducing
the number of tests from 1300 to 430.
