[Bug target/106585] RISC-V: Mis-optimized code gen for zbs

[kito at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106585

--- Comment #5 from Kito Cheng <kito at gcc dot gnu.org> ---
bset generated after change X to GPR for most zbs pattern:

```
foo:
        bset    a1,x0,a1
        andn    a0,a0,a1
        sext.w  a0,a0
        ret

```