Kernel: Move aarch64 Prekernel into Kernel

As there is no need for a Prekernel on aarch64, the Prekernel code was
moved into Kernel itself. The functionality remains the same.

SERENITY_KERNEL_AND_INITRD in run.sh specifies a kernel and an inital
ramdisk to be used by the emulator. This is needed because aarch64
does not need a Prekernel and the other ones do.

Kernel/Arch/aarch64/PrekernelCommon.cpp

@@ -0,0 +1,32 @@
+/*
+ * Copyright (c) 2021, James Mintram <me@jamesrm.com>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <Kernel/Arch/aarch64/Prekernel.h>
+
+#include <Kernel/Arch/aarch64/ASM_wrapper.h>
+#include <Kernel/Arch/aarch64/UART.h>
+
+namespace Prekernel {
+
+[[noreturn]] void panic(const char* msg)
+{
+    auto& uart = Prekernel::UART::the();
+
+    if (msg) {
+        uart.print_str(msg);
+    }
+
+    Prekernel::halt();
+}
+
+[[noreturn]] void halt()
+{
+    for (;;) {
+        asm volatile("wfi");
+    }
+}
+
+}