Kernel: Remove trap based syscall handling

This patch removes the x86 mechanism for calling syscalls, favoring
the more modern syscall instruction. It also moves architecture
dependent code from functions that are meant to be architecture
agnostic therefore paving the way for adding more architectures.

Kernel/API/Syscall.h

@@ -9,6 +9,7 @@
 #include <AK/Types.h>
 #include <AK/Userspace.h>
 #include <Kernel/API/POSIX/sched.h>
+#include <Kernel/Arch/RegisterState.h>
 
 constexpr int syscall_vector = 0x82;
 
@@ -201,6 +202,8 @@ enum class NeedsBigProcessLock {
 
 namespace Syscall {
 
+ErrorOr<FlatPtr> handle(RegisterState&, FlatPtr function, FlatPtr arg1, FlatPtr arg2, FlatPtr arg3, FlatPtr arg4);
+
 enum Function {
 #undef __ENUMERATE_SYSCALL
 #define __ENUMERATE_SYSCALL(sys_call, needs_lock) SC_##sys_call,