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/BootPPMParser.h

@@ -0,0 +1,38 @@
+/*
+ * Copyright (c) 2021, Marcin Undak <mcinek@gmail.com>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/Types.h>
+
+namespace Prekernel {
+
+// Quick parser for .ppm image format (raw PortablePixMap)
+// This is much simpler version than userland implementation in PPMLoader.cpp
+class BootPPMParser {
+public:
+    struct {
+        u32 width = 0;
+        u32 height = 0;
+        u8 const* pixel_data = nullptr;
+    } image;
+
+    BootPPMParser(u8 const* buffer, u32 buffer_size);
+
+    bool parse();
+
+private:
+    char const* m_cursor;
+    char const* m_buffer_end;
+
+    bool check_position() const;
+    bool parse_magic();
+    bool parse_new_line();
+    bool parse_comment();
+    bool parse_integer(u32& value);
+};
+
+}