ARM: use common macro template for bilinear scaled 'src_8888_8888'

ARM: use common macro template for bilinear scaled 'src_8888_8888'

This is a cleanup for old and now duplicated code. The performance improvement
is mostly coming from the enabled use of software prefetch, but instructions
scheduling is also slightly better.

Benchmark on ARM Cortex-A8 r2p2 @1GHz, 32-bit LPDDR @200MHz:
 Microbenchmark (scaling 2000x2000 image with scale factor close to 1x):
  before: op=1, src=20028888, dst=20028888, speed=53.24 MPix/s
  after:  op=1, src=20028888, dst=20028888, speed=74.36 MPix/s