dump x86 CPUID info up to page 02h

And reject CPUs that don't have a FPU. (untested, ha ha.)
testbench: x86: add MMX smoketest

Seems to work just fine, which is logical as MMX state is completely
transparent to the OS kernel.
testbench: x86: add SSE smoketest

And enable SSE instructions in the Makefile. Or rather, stop disabling them.
cpu: add SSE support, re-/store of SSE state
testbench: x86: add SSE context restore test

This tests the mechanism as far as the control word is concerned. Appropriate
breakage is demonstrated by removal of x86_fxsave()/x86_fxrstor() calls from
the #NM handler.