Kernel/Graphics: Allocate VGA window region according to the usual rules

We should not allocate a kernel region inside the constructor of the
VGATextModeConsole class. We do use MUST() because allocation cannot
fail at this point, but that happens in the static factory method
instead.

Kernel/Graphics/Console/VGATextModeConsole.h

@@ -36,7 +36,7 @@ public:
 private:
     void clear_vga_row(u16 row);
 
-    VGATextModeConsole();
+    explicit VGATextModeConsole(NonnullOwnPtr<Memory::Region>);
 
     mutable Spinlock m_vga_lock;