configs: use different types for .Devices and .Resources.Devices

Making them the same type is simply confusing, but also means that you
could accidentally use one in the wrong context. This eliminates that
problem. This also includes a whole bunch of cleanups for the types
within DeviceRule, so that they can be used more ergonomically.

Signed-off-by: Aleksa Sarai <asarai@suse.de>

libcontainer/cgroups/fs2/devices.go

@@ -10,12 +10,10 @@ import (
 	"golang.org/x/sys/unix"
 )
 
-func isRWM(cgroupPermissions string) bool {
-	r := false
-	w := false
-	m := false
-	for _, rn := range cgroupPermissions {
-		switch rn {
+func isRWM(perms configs.DevicePermissions) bool {
+	var r, w, m bool
+	for _, perm := range perms {
+		switch perm {
 		case 'r':
 			r = true
 		case 'w':