Kernel: Be more clever with physical memory

Initially allocate all physical memory except kernel memory and boot
modules. Before we just skipped all memory before kernel boot modules.
Also release memory used by boot modules after the kernel is up and
running. Once the boot modules are loaded, there is no need to keep them
in memory.

kernel/include/kernel/Memory/Heap.h

@@ -18,6 +18,8 @@ namespace Kernel
 		static void initialize();
 		static Heap& get();
 
+		void release_boot_modules();
+
 		paddr_t take_free_page();
 		void release_page(paddr_t);