[llvm] [RISCV][TTI] Enable masked interleave vectorization (PR #150074)

[Philip Reames via llvm-commits]

preames wrote:

> Just checking, this sets out to do the same thing as #149981 right?

It appears to mostly cover the same ground.  I prefer my version for a number of small reasons, but I'd not have posted it if I'd seen that first.  I'd have just replied there with detailed comments.

https://github.com/llvm/llvm-project/pull/150074