ARMv6: New conversion routines

ARMv6: New conversion routines

There was no previous attempt at accelerating these specifically for
ARMv6.

src_x888_8888

    Before          After
    Mean   StdDev   Mean   StdDev  Confidence  Change
L1  96.7   0.5      270.4  2.6     100.0%      +179.5%
L2  44.6   2.7      110.6  9.7     100.0%      +148.0%
M   26.9   0.1      87.6   0.5     100.0%      +226.1%
HT  19.3   0.2      37.5   0.4     100.0%      +93.7%
VT  18.6   0.1      33.7   0.4     100.0%      +81.6%
R   18.4   0.1      32.2   0.3     100.0%      +75.2%
RT  9.2    0.2      12.1   0.3     100.0%      +31.4%

src_0565_8888

    Before          After
    Mean   StdDev   Mean   StdDev  Confidence  Change
L1  37.0   0.3      66.9   0.2     100.0%      +80.8%
L2  30.3   0.2      55.9   0.3     100.0%      +84.4%
M   25.9   0.0      62.3   0.2     100.0%      +140.3%
HT  15.2   0.1      33.1   0.3     100.0%      +116.9%
VT  15.1   0.1      30.7   0.3     100.0%      +103.6%
R   14.2   0.1      27.6   0.3     100.0%      +94.0%
RT  6.0    0.1      11.2   0.3     100.0%      +87.2%