vmm(4): set RAX guest register state based on VMCB

vmm(4): set RAX guest register state based on VMCB

The read/write register routines for SVM didn't acknowledge RAX in
the VMCB as the de facto RAX state. When writing gprs, vmm should
update RAX in the VMCB. When reading, it should be setting the guest
regs state based on the VMCB.

Needed for proper mmio emulation in userland.

ok mlarkin@