fix(instructions): allow unused_unsafe for cpuid

[mkroening]

While rust-lang/stdarch#1935 has not reached stable yet, on nightly, Clippy makes the CI fail:

warning: unnecessary `unsafe` block
  --> src/instructions/random.rs:13:21
   |
13 |         let cpuid = unsafe { core::arch::x86_64::__cpuid(0x1) };
   |                     ^^^^^^ unnecessary `unsafe` block
   |
   = note: `#[warn(unused_unsafe)]` (part of `#[warn(unused)]`) on by default

warning: unnecessary `unsafe` block
  --> src/instructions/smap.rs:38:21
   |
38 |         let cpuid = unsafe { core::arch::x86_64::__cpuid(7) };
   |                     ^^^^^^ unnecessary `unsafe` block

warning: unnecessary `unsafe` block
   --> src/instructions/tlb.rs:163:21
    |
163 |         let cpuid = unsafe { core::arch::x86_64::__cpuid(0x8000_0008) };
    |                     ^^^^^^ unnecessary `unsafe` block

warning: unnecessary `unsafe` block
   --> src/instructions/tlb.rs:172:21
    |
172 |         let cpuid = unsafe { core::arch::x86_64::__cpuid(0x8000_000a) };
    |                     ^^^^^^ unnecessary `unsafe` block

Please let me know if you would like to have this conditional or whether I should add a comment. :)

Note that this might not be intentional and may be fixed in the future: rust-lang/stdarch#1990