imagetools: use dockerconfig for auth

Enables fallback for DHI and Scout registries and
repo/scope specific credentials like supported for builds.

Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>

driver/driver.go

@@ -8,7 +8,6 @@ import (
 
 	"github.com/docker/buildx/store"
 	"github.com/docker/buildx/util/progress"
-	clitypes "github.com/docker/cli/cli/config/types"
 	controlapi "github.com/moby/buildkit/api/services/control"
 	"github.com/moby/buildkit/client"
 	"github.com/pkg/errors"
@@ -58,10 +57,6 @@ type Info struct {
 	DynamicNodes []store.Node
 }
 
-type Auth interface {
-	GetAuthConfig(registryHostname string) (clitypes.AuthConfig, error)
-}
-
 type Driver interface {
 	Factory() Factory
 	Bootstrap(context.Context, progress.Logger) error