x86: cacheline_align tss_struct

The manual padding to align on cacheline size only worked in 32 bit
In 64 bit the structure was not aligned and contained wasted space.

use the compiler ____cachline_aligned to save space & properly align
this structure.

x86_64_default size goes from 9136 -> 8960
x86_64_AMD     size goes from 9136 -> 8896

built & running on 2.6.26-rc8.

Signed-off-by: Richard Kennedy <richard@rsk.demon.co.uk>
Signed-off-by: Ingo Molnar <mingo@elte.hu>