diag/memory: Support refined return value about textual updates

Support three different return values on memory_test_run() for reducing
screen redrawing delay.
- VB2_SUCCESS: The test is finished and there may have been a textual
update.
- VB2_ERROR_EX_DIAG_TEST_RUNNING: the test is still running but there
were no textual updates.
- VB2_ERROR_EX_DIAG_TEST_UPDATED: the test is still running and there
were textual updates.

BUG=b:168776970
BRANCH=none
TEST=Build locally, boot recovery, select 'run diagnostics',
     enter memory test (full) screen,
     and observe that the delay reduces while pressing keyboard

Cq-Depend: chromium:2424370
Signed-off-by: Hsuan Ting Chen <roccochen@chromium.org>
Change-Id: Idf958e917c6b0f0fa798cb1c9704efa20ee2d6e5
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/depthcharge/+/2423699
2 files changed