Add mutex to Vga console to satisfy console.Console

kernel/driver/video/console/vga.go

@@ -2,6 +2,7 @@ package console
 
 import (
 	"reflect"
+	"sync"
 	"unsafe"
 )
 
@@ -15,6 +16,8 @@ const (
 // allocator, each console will use its own framebuffer while the active console
 // will periodically sync its internal buffer with the physical screen buffer.
 type Vga struct {
+	sync.Mutex
+
 	width  uint16
 	height uint16