Kernel: Simplify graphics initialization somewhat

We use a switch-case statements to ensure we try to find the best
suitable driver for a specific graphics card. In case we don't find
such, we use the default statement to initialize the graphics card as a
generic VGA adapter, if the adapter is VGA compatible.

If we couldn't initialize the driver, we don't touch this adapter
anymore.

Also, GraphicsDevice should not be tied to a PCI::Address member, as it
can be theortically be used with other buses (e.g. ISA cards).

Kernel/Graphics/GraphicsManagement.h

@@ -47,6 +47,7 @@ public:
     void activate_graphical_mode();
 
 private:
+    bool determine_and_initialize_graphics_device(const PCI::Address& address, PCI::ID id);
     NonnullRefPtrVector<GraphicsDevice> m_graphics_devices;
     NonnullOwnPtr<Region> m_vga_font_region;
     RefPtr<Graphics::Console> m_console;