i386 gdt and percpu cleanups

Hi Andi,

This is a series of patches based on your latest queue (as of the
other day, at least).

It includes:
 - the most recent patch to compute the appropriate amount of percpu
   space to allocate, using a separate reservation for modules where
   needed.
 - make the percpu sections page-aligned, so that percpu variables can
   be page aligned if needed (which is used by gdt_page)
 - page-align the gdt
 - remove the pda and convert all pda usages into percpu variables
   (percpu variables still use the %fs prefix mechanism the pda used)
 - some improvements to asm-i386/percpu.h to make asm access to percpu
   variables easy
 - define per_cpu_offset in asm-i386/percpu.h, to match asm-generic/

Thanks,
	J

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