Actually replace the numeric values by the new symbolic values.

I used this to find all the existing users of the GDT_ENTRY*() macros:

  $ git grep -P 'GDT_ENTRY(_INIT)?\('

Some of the lines will exceed 80 characters, but some of them will be
shorter again in the next couple of patches.
Signed-off-by: Vegard Nossum <vegard.nossum@oracle.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/r/20231219151200.2878271-4-vegard.nossum@oracle.com