vboot/ui: move locale_id from screen_state into ui_context

locale_id is not tied to the current screen -- i.e. it shouldn't
revert if we return to the previous screen.

TEST=make clean && make runtests

Change-Id: I691bdf7938d2a14cfbe68c7f60dc0103c236733c
Signed-off-by: Joel Kitching <kitching@google.com>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/vboot_reference/+/2182083
Tested-by: Hsuan Ting Chen <roccochen@chromium.org>
Tested-by: Joel Kitching <kitching@chromium.org>
Reviewed-by: Joel Kitching <kitching@chromium.org>
Commit-Queue: Joel Kitching <kitching@chromium.org>
4 files changed