[boot][kernel] Replace frame allocator with bitmap-based one

The previous frame allocator involved a lot of splitting and merging
linked lists and lost all information about frames while they were
allocated. The new allocator is based on an array of descriptor
structures and a bitmap. Each memory map region of allocatable memory
becomes one or more descriptors, each mapping up to 1GiB of physical
memory. The descriptors implement two levels of a bitmap tree, and have
a pointer into the large contiguous bitmap to track individual pages.

src/boot/main.cpp

@@ -191,11 +191,14 @@ efi_main(uefi::handle image, uefi::system_table *st)
 	args->video = con.fb();
 	status_bar status {con.fb()}; // Switch to fb status display
 
+	// Map the kernel to the appropriate address
 	args::program &kernel = args->programs[0];
 	for (auto &section : kernel.sections)
 		if (section.size)
 			paging::map_section(args, section);
 
+	memory::fix_frame_blocks(args);
+
 	kernel::entrypoint kentry =
 		reinterpret_cast<kernel::entrypoint>(kernel.entrypoint);
 	status.next();