libpayload/xhci: Document struct offsets on xhci_t

This makes it easier to know what offset each register references.

BUG=b:76831439
TEST=none

Change-Id: I92dcbd463ceb4dd8edbbd97b51a4e9aa32a983a6
Signed-off-by: Raul E Rangel <rrangel@chromium.org>
Reviewed-on: https://review.coreboot.org/27474
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
1 file changed