[llvm] Fix movk on aarch64 with an .equ operand (PR #124428)

[Fangrui Song via llvm-commits]

MaskRay wrote:

The tests are not very well-organized. I might use rg to find relevant tests
```
% rg 'movk.*lsl' llvm/test/MC/AArch64/
llvm/test/MC/AArch64/basic-a64-instructions.s
3346:        movk xzr, #4321, lsl #48
3348:// CHECK: movk     xzr, #{{4321|0x10e1}}, lsl #48 // encoding: [0x3f,0x1c,0xe2,0xf2]
```

Perhaps use basic-a64-instructions.s in the absence of better tests.

https://github.com/llvm/llvm-project/pull/124428