base/timestamp: Add function to get tick frequency

Port timestamp_tick_freq_mhz() from coreboot.

BUG=b:305902595
TEST=Verify build and boot on Screebo

Change-Id: I0303bab1b14f5e8cbc62342070013460b748e2dc
Signed-off-by: Kapil Porwal <kapilporwal@google.com>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/depthcharge/+/5640813
Tested-by: Kapil Porwal <kapilporwal@chromium.org>
Reviewed-by: Subrata Banik <subratabanik@chromium.org>
Commit-Queue: Kapil Porwal <kapilporwal@chromium.org>
2 files changed