ramstage: remove rela_time use

mono_time_diff_microseconds() is sufficient for determining
the microsecond duration between 2 monotonic counts.

BUG=None
BRANCH=None
TEST=Built and booted. Bootstate timings still work.

Change-Id: I7b9eb16ce10fc91bf515c5fc5a6f7c80fdb664eb
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/219711
Reviewed-by: Duncan Laurie <dlaurie@chromium.org>
Reviewed-by: Furquan Shaikh <furquan@chromium.org>
1 file changed