x86: Remove MIN_PORT80_KCLOCKS_DELAY

This is not referenced anywhere. Remove it, as well as
tsc_base_kclocks and tsc_prev in the global data.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Acked-by: Simon Glass <sjg@chromium.org>
Fix 'Reomve' typo:
Signed-off-by: Simon Glass <sjg@chromium.org>