[llvm] [GISel] Restrict G_BSWAP to multiples of 16 bits. (PR #70245)

[Evgenii Kudriashov via llvm-commits]

================
@@ -4,35 +4,6 @@
 
 # test bswap for s16, s17, s32, and s64
 
-...
----
-name:            test_bswap17
----------------
e-kud wrote:

Yeah, `X86` implementation was copied from `AArch64` that also fails on the following mir with the same assert
```
 %0:_(s48) = IMPLICIT_DEF
 %1:_(s16), %2:_(s16), %3:_(s16) = G_UNMERGE_VALUES %0:_(s48)
 %4:_(s32) = G_ANYEXT %1(s16)
 $w0 = COPY %4(s32)
 RET_ReallyLR implicit $w0
```

https://github.com/llvm/llvm-project/pull/70245