Added bitmap_t type and bmap_* functions & used them in PMM

kernel/include/bitmap.h

@@ -0,0 +1,23 @@
+#ifndef _BITMAP_H
+#define _BITMAP_H
+
+#include <kernel.h>
+
+#define BLOCK_SIZE	4096
+#define BMAP_NOT_FOUND	((size_t)-1)
+
+typedef struct bitmap_t {
+	void* map;
+	size_t blocks;	// Eqiv. to # of bits
+	size_t bytes;	// ceil(blocks / 8)
+	size_t used;	// # of bits set to 0
+	int ready;
+} bitmap_t;
+
+void	bmap_set(bitmap_t* map, size_t bit, int val);
+int	bmap_get(bitmap_t* map, size_t bit);
+void	bmap_setarea(bitmap_t* map, size_t base, size_t len, int val);
+void	bmap_setall(bitmap_t* map, int val);
+size_t	bmap_findarea(bitmap_t* map, size_t len, int val);
+
+#endif