PcAtChipsetPkg/PcRtc: Fix a Y2K bug

PcAtChipsetPkg/PcRtc: Fix a Y2K bug

The original driver cannot handle the case when system time runs from 1999/12/31 23:59:59
to 2000/1/1 0:0:0.
A simple test to set system time to 1999/12/31 23:59:59 can expose this bug.
The patch limits the driver to only support year in 100 range and decide the century value based
on the supporting range: Century either equals to PcdMinimalYear / 100 or equals to PcdMinimalYear / 100 + 1.

The patch passed the Y2K test.
However with year range [1998, 2097], when system time is 2097/12/31 23:59:59,
the next second system time will become 1998/1/1 0:0:0. I think it's a acceptable limitation.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ruiyu Ni <ruiyu.ni@intel.com>
Reviewed-by: Feng Tian <feng.tian@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@17624 6f19259b-4bc3-4df7-8a09-765794883524