[SVE][CodeGen] Fix bug with store of unpacked FP scalable vectors

Fixed an incorrect pattern in lib/Target/AArch64/AArch64SVEInstrInfo.td
for storing out <vscale x 2 x f32> unpacked scalable vectors. Added
a couple of tests to

  test/CodeGen/AArch64/sve-st1-addressing-mode-reg-imm.ll

Differential Revision: https://reviews.llvm.org/D85441