firmware: coreboot: Only populate devices in coreboot_table_init()

This function checks the header for sanity, registers a bus, and
populates devices for each coreboot table entry. Let's just populate
devices here and pull the other bits up into the caller so that this
function can be repurposed for pure device creation and registration.

Cc: Wei-Ning Huang <wnhuang@chromium.org>
Cc: Julius Werner <jwerner@chromium.org>
Cc: Brian Norris <briannorris@chromium.org>
Cc: Samuel Holland <samuel@sholland.org>
Suggested-by: Julius Werner <jwerner@chromium.org>
Signed-off-by: Stephen Boyd <swboyd@chromium.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>