[RISCV] Add test cases to show that rvv_vector_bits attribute is not accepted...

[RISCV] Add test cases to show that rvv_vector_bits attribute is not accepted for vbool or LMUL!=1 RVV types. NFC

The error message isn't great, but it's temporary until we support these.

Reviewed By: aaron.ballman

Differential Revision: https://reviews.llvm.org/D152415