PMM: init (find biggest usable region)

src/mem/paging/pmm.h

@@ -0,0 +1,16 @@
+#ifndef PAGING_PMM_H
+#define PAGING_PMM_H
+
+#include <limine.h>
+
+void pmm_init(struct limine_memmap_response* memmap, struct limine_hhdm_response* hhdm);
+
+// Might be upgraded to a freelist later.
+// For now, we can take the biggest usable region and we will be fine.
+struct usable_memory
+{
+    uint64_t base; // physical
+    uint64_t length;
+};
+
+#endif