Refactor USB code which will be reused among similar SoCs.
BUG=b:80501386
BRANCH=none
TEST=Boots correctly on Elm
Change-Id: I06fefb4149a489be991e13ddf624082d11e31765
Signed-off-by: Tristan Shieh <tristan.shieh@mediatek.com>
Reviewed-on: https://review.coreboot.org/28786
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Hung-Te Lin <hungte@chromium.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>