all: BITALG instructions (#362)

Adds the AVX-512 Bit Algorithms instruction set.

These new instructions are added via the `opcodesextra` mechanism #345, since
they're missing from the opcodes database.

Contributed by @vsivsi. Extracted from #234 with simplifications for AVX-512
form expansion.

Co-authored-by: Vaughn Iverson <vsivsi@yahoo.com>

internal/opcodesextra/instructions.go

@@ -11,6 +11,7 @@ var sets = [][]*inst.Instruction{
 	vnni,
 	vpclmulqdq,
 	vpopcntdq,
+	bitalg,
 }
 
 // Instructions returns a list of extras to add to the instructions database.