Add initial infrastructure for usermode replay project

This adds an initial radeon_replay program which replays the trace
obtained on an HP Pavilion m6 1035dx laptrop. The trace was converted
to C code using the util/cb2replay script, and the IO helpers were
moved to a separate file.

Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
radeon_replay: Add VGA IO helpers

These are pulled verbatim from the coreboot tree.

Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>