Work on graphics/mem

- Add BUDDY_INDEX() helper macro
- Add release_block() API
	- Coalesces freed blocks on call, as much as possible
- Fix should/do_coalesce(); blk param now pointer to array of MAX_BLOCKS
  mem_blk elements.
- Added test_full_release_order() test routine to graphics/mem unit test
	- Rework test to call this after test_full_alloc_order() calls