Some clean up of the segment selectors macros
Some clean up of the segment selectors macros

- [ABCD]_INDEX are not used anywhere

- value of *_SELECTOR is now calculated using the *_INDEX value so changing the
  index does not break the selector

- TSS is now the last of the global selectors. There will be TSS per CPU on SMP
  and the number will vary depending on the maximal supported number of CPUs
  configured



veritas-shine/minix3-rpi,veritas-shine/minix3-rpi,veritas-shine/minix3-rpi,veritas-shine/minix3-rpi,veritas-shine/minix3-rpi,veritas-shine/minix3-rpi,veritas-shine/minix3-rpi,veritas-shine/minix3-rpi