Set default CR) so that the FPU is enabled (unset CR0_EM) and initialise
i386_fpu_present to 1.
No need to call the npx trap indirectly, rename to fpunda() to match amd64.
Remove the i386_fpu_exception variable and sysctl (It used to indicate
which irq was used for fpu exceptions, but we only support 'internal'
now). Hopefully no one cares.
fpuinit() now only needs to clear TS before the fninit(). Apart from the
checks for 486SX and the 'fdiv bug' this matches the amd64 version.
Exclude fpuinit() from XEN kernels, they don't call it - which rather begs
the question as to whether it is needed at all!
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