Kernel/Graphics: Move x86-specific support for VGA to Arch/x86 directory

The new VGAIOArbiter class is now responsible to conduct x86-specific
instructions to control VGA hardware from the old ISA ports. This allows
us to ensure the GraphicsManagement code doesn't use x86-specific code,
thus allowing it to be compiled within non-x86 kernel builds.

Kernel/CMakeLists.txt

@@ -344,6 +344,8 @@ if ("${SERENITY_ARCH}" STREQUAL "i686" OR "${SERENITY_ARCH}" STREQUAL "x86_64")
         Arch/x86/PCI/Controller/HostBridge.cpp
         Arch/x86/PCI/IDELegacyModeController.cpp
         Arch/x86/PCI/Initializer.cpp
+
+        Arch/x86/VGA/IOArbiter.cpp
     )
 
     set(KERNEL_SOURCES