ARM: better NEON instructions scheduling for over_n_8_0565

ARM: better NEON instructions scheduling for over_n_8_0565

Code rearranged to get better instructions scheduling for ARM Cortex-A8/A9.
Now it is ~30% faster for the pixel data in L1 cache and makes better use
of memory bandwidth when running at lower clock frequencies (ex. 500MHz).
Also register d24 (pixels from the mask image) is now not clobbered by
supplementary macros, which allows to reuse them for the other variants
of compositing operations later.

Benchmark from ARM Cortex-A8 @500MHz:

== before ==

    over_n_8_0565 =  L1:  63.90  L2:  63.15  M: 60.97 ( 73.53%)
                     HT:  28.89  VT:  24.14  R: 21.33  RT:  6.78 (  67Kops/s)

== after ==

    over_n_8_0565 =  L1:  82.64  L2:  75.19  M: 71.52 ( 84.14%)
                     HT:  30.49  VT:  25.56  R: 22.36  RT:  6.89 (  68Kops/s)