cpufeatures: add support for detecting AVX-512 (#862)

Adds support for detecting the following features:

- `avx512f`
- `avx512dq`
- `avx512ifma`
- `avx512pf`
- `avx512er`
- `avx512cd`
- `avx512bw`
- `avx512vl`

CPUID bitflags obtained from this table:

https://en.wikichip.org/wiki/x86/avx-512#Detection

Closes #815

Author: tarcieri

cpufeatures/src/x86.rs

@@ -99,7 +99,15 @@ __expand_check_macro! {
     ("bmi1", 1, ebx, 3),
     ("avx2", 0, ecx, 28, 1, ebx, 5),
     ("bmi2", 1, ebx, 8),
+    ("avx512f", 1, ebx, 16),
+    ("avx512dq", 1, ebx, 17),
     ("rdseed", 1, ebx, 18),
     ("adx", 1, ebx, 19),
+    ("avx512ifma", 1, ebx, 21),
+    ("avx512pf", 1, ebx, 26),
+    ("avx512er", 1, ebx, 27),
+    ("avx512cd", 1, ebx, 28),
     ("sha", 1, ebx, 29),
+    ("avx512bw", 1, ebx, 30),
+    ("avx512vl", 1, ebx, 31),
 }