ARM: VIXL32: Move code to ease the diff with old codegen.

This patch doesn't change anything except relocation the code
to preserve original order of functions as in code_generator_arm.cc
to make it easier to review and to fulfill comparison of two arm
backends for reaching the parity between them.

Test: export ART_USE_VIXL_ARM_BACKEND=true && \
      mma test-art-host dist && \
      mma test-art-target dist

Change-Id: I6c3a84f5606069a795d4d8122fc0d4a308e2b7ec