all: AVX-512 (#217)

Extends avo to support most AVX-512 instruction sets.

The instruction type is extended to support suffixes. The K family of opmask
registers is added to the register package, and the operand package is updated
to support the new operand types. Move instruction deduction in `Load` and
`Store` is extended to support KMOV* and VMOV* forms.

Internal code generation packages were overhauled. Instruction database loading
required various messy changes to account for the additional complexities of the
AVX-512 instruction sets. The internal/api package was added to introduce a
separation between instruction forms in the database, and the functions avo
provides to create them. This was required since with instruction suffixes there
is no longer a one-to-one mapping between instruction constructors and opcodes.

AVX-512 bloated generated source code size substantially, initially increasing
compilation and CI test times to an unacceptable level. Two changes were made to
address this:

1.  Instruction constructors in the `x86` package moved to an optab-based
    approach. This compiles substantially faster than the verbose code
    generation we had before.

2.  The most verbose code-generated tests are moved under build tags and
    limited to a stress test mode. Stress test builds are run on
    schedule but not in regular CI.

An example of AVX-512 accelerated 16-lane MD5 is provided to demonstrate and
test the new functionality.

Updates #20 #163 #229

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

internal/gen/godata.go

@@ -1,6 +1,7 @@
 package gen
 
 import (
+	"github.com/mmcloughlin/avo/internal/api"
 	"github.com/mmcloughlin/avo/internal/inst"
 	"github.com/mmcloughlin/avo/internal/prnt"
 	"github.com/mmcloughlin/avo/printer"
@@ -57,8 +58,21 @@ func (g *godata) Generate(is []inst.Instruction) ([]byte, error) {
 				g.Printf("},\n")
 			}
 
-			if f.CancellingInputs {
-				g.Printf("CancellingInputs: true,\n")
+			g.Printf("EncodingType: %#v,\n", f.EncodingType)
+
+			for _, flag := range []struct {
+				Field   string
+				Enabled bool
+			}{
+				{"CancellingInputs", f.CancellingInputs},
+				{"Zeroing", f.Zeroing},
+				{"EmbeddedRounding", f.EmbeddedRounding},
+				{"SuppressAllExceptions", f.SuppressAllExceptions},
+				{"Broadcast", f.Broadcast},
+			} {
+				if flag.Enabled {
+					g.Printf("%s: true,\n", flag.Field)
+				}
 			}
 
 			g.Printf("},\n")
@@ -90,6 +104,7 @@ func NewGoDataTest(cfg printer.Config) Interface {
 
 func (g *godatatest) Generate(is []inst.Instruction) ([]byte, error) {
 	g.Printf("// %s\n\n", g.cfg.GeneratedWarning())
+	g.NL()
 	g.Printf("package inst_test\n\n")
 
 	g.Printf(`import (
@@ -98,7 +113,7 @@ func (g *godatatest) Generate(is []inst.Instruction) ([]byte, error) {
 
 		"%s/internal/inst"
 	)
-	`, pkg)
+	`, api.Package)
 
 	g.Printf("var raw = %#v\n\n", is)