[boot] Load programs in boot, not kernel

Remove ELF and initrd loading from the kernel. The bootloader now loads
the initial programs, as it does with the kernel. Other files that were
in the initrd are now on the ESP, and non-program files are just passed
as modules.

src/boot/types.h

@@ -0,0 +1,13 @@
+/// \file types.h
+/// Definitions of shared types used throughout the bootloader
+#pragma once
+
+namespace boot {
+
+struct buffer
+{
+	size_t size;
+	void *data;
+};
+
+} // namespace boot