amd64 miniport drivers are allowed to use FPU which triggers "Unregistered use
of FPU in kernel" panic.
Wrap all variants of MSCALL with fpu_kern_enter/fpu_kern_leave. To reduce
amount of allocations/deallocations done via
fpu_kern_alloc_ctx/fpu_kern_free_ctx maintain cache of fpu_kern_ctx elements.
Based on the patch by Paul B Mahol
PR: 165622
Submitted by: Vlad Movchan <vladislav.movchan@gmail.com>
MFC after: 1 month
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