ARM64: Support SVE VL other than 128-bit.

Arm SVE register size is not fixed and can be a
multiple of 128 bits. To support that the patch
removes explicit assumptions on the SIMD register
size to be 128 bit from the vectorizer and code
generators and enables configurable SVE vector
length autovectorization, e.g. extends SIMD register
save/restore routines.

Test: art SIMD tests on VIXL simulator.
Test: art tests on FVP (steps in test/README.arm_fvp.md)
      with FVP arg:
      -C SVE.ScalableVectorExtension.veclen=[2,4]
      (SVE vector [128,256] bits wide)

Change-Id: Icb46e7eb17f21d3bd38b16dd50f735c29b316427
11 files changed