Code consolidation

[sigma]

This is an attempt at reorganizing the code in a platform/arch friendly way

This essentially does the following:

• add a few arch-agnostic interfaces to registers
• make use of them to eliminate most differences between amd64 and 386 algorithms
• consolidate the common parts in non-arch-specific source files

It also isolates the platform-specific part of vmcheck so that other platforms only have to provide a single function (hopefully)

This is not tested properly right now, but any feedback is welcome @frapposelli @dougm @fdawg4l

[dougm]

@sigma nice! lgtm, I've tested your branch using toolbox-test.sh on amd64: https://github.com/vmware/govmomi/tree/master/toolbox#testing