[RISCV] Add codegen tests for vector.(de)interleave3/5/7 on FP scalable vectors (llvm#137257)

We had `vector.(de)interleave3/5/7` tests for floating point fixed
vectors but not for scalable vectors. This patch adds some tests. I also
reorganized the test files so all integer tests are put at the top.

Author: mshockwave