Kernel/aarch64: Implement initial page fault handling

The shared code is moved to a common PageFault.cpp file.

Kernel/Arch/PageFault.h

@@ -8,6 +8,7 @@
 
 #include <AK/Platform.h>
 #include <AK/Types.h>
+#include <Kernel/Arch/RegisterState.h>
 #include <Kernel/ExecutionMode.h>
 #include <Kernel/VirtualAddress.h>
 
@@ -44,6 +45,8 @@ public:
     {
     }
 
+    void handle(RegisterState& regs);
+
     enum class Type {
         PageNotPresent = PageFaultFlags::NotPresent,
         ProtectionViolation = PageFaultFlags::ProtectionViolation,