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     - adds ability to find some of rt-features the _cpu_ supports. In
       particular if xsave insn is supported we need to know how big memory
       slab is needed to keep complete fpu frame

this gives us the size of fpu frame. Moreover, since we need to call cpuid
anyway, we do a fast early check for features we need from cpuid results.
If we have bits needed on hw level, we still need to check if kernel was not booted
with "nofxsr", which disables fxsave instruction and prevents us from continue
working, if everything is fine -- we can do restore.

	Cyrill