[SLP]Initial support for interleaved loads
Adds initial support for interleaved loads, which allows
emission of segmented loads for RISCV RVV.
Vectorizes extra code for RISCV
CFP2006/447.dealII, CFP2006/453.povray,
CFP2017rate/510.parest_r, CFP2017rate/511.povray_r,
CFP2017rate/526.blender_r, CFP2017rate/538.imagick_r, CINT2006/403.gcc,
CINT2006/473.astar, CINT2017rate/502.gcc_r, CINT2017rate/525.x264_r
Reviewers: RKSimon, preames
Reviewed By: preames
Pull Request: https://github.com/llvm/llvm-project/pull/112042