x86_emulate: (Almost) complete FPU emulation.

x86_emulate: (Almost) complete FPU emulation.

Provide emulation for all FPU instructions except fsave/frstore &
fnstenv/fldenv.

While the main purpose of the patch is to avoid current and future
"gotchas" on FPU intructions used by various OS boot-loaders, it is
complete enough to run DOS realmode FPU applications and benchmarks,
but don't expect to set any speed records.

Signed-off-by: Trolle Selander <trolle.selander@eu.citrix.com>
Signed-off-by: Keir Fraser <keir.fraser@citrix.com>