Makefile changes by Sam Ravnborg. Summary of changes:
o Added FORCE prerequisite in boot/Makefile
o Do not use shorthand targets when calling the boot/Makefile
o No longer use BOOT_IMAGE, not needed now
o Use kbuild clean infrastructure when cleaning up in boot
o Offset generation shrinked with one rule
o removed inclusion of Rules.make in all Makefiles
o no longer use the descend macro, use $(Q)$(MAKE) as replacement