x86: cleanup - eliminate numbers in LDT allocation code

This patch eliminates numbers in LDT allocation code
trying to make it clear to understand from where
these numbers come.

No code changed:

   text    data     bss     dec     hex filename
   1896       0       0    1896     768 ldt.o.before
   1896       0       0    1896     768 ldt.o.after
md5:
 6cbec8705008ddb4b704aade60bceda3  ldt.o.before.asm
 6cbec8705008ddb4b704aade60bceda3  ldt.o.after.asm

Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>