Change the strategy for using the FPU in the kernel. The kernel FPU state

Change the strategy for using the FPU in the kernel.  The kernel FPU state
is now shared with all processes/threads.  As a result, you can now use the
FPU in true process context (instead of just in kernel threads), but you
need to make sure you restore the default FPU state before calling
fpu_kernel_exit() if you change rounding mode, precision or exception masks.

Lots of discussion with thib@ and Mike Belopuhov.

ok thib@, deraadt@