[memory layout] streamline memory layout

Memory layout can now be specified via kconfig options. Two
possibilities exist: default layout means the layout is stack
/ malloc heap / U-Boot. The user can also specify fixed addresses
for each TEXT_BASE / stack / malloc heap.

board/at91sam9260ek/config.h

@@ -1,2 +1,4 @@
-#define CFG_MALLOC_LEN             (4096 << 10)
-#define CONFIG_STACKSIZE    (32 * 1024)     /* regular stack */
+#ifndef __CONFIG_H
+#define __CONFIG_H
+
+#endif	/* __CONFIG_H */