PcAtChipsetPkg/PcRtc: get century RTC address in entry point

PcAtChipsetPkg/PcRtc: get century RTC address in entry point

When ACPI table is installed before PcRtc driver runs,
the ACPI table installation callback isn't called which causes the
century value isn't written to the CMOS.
The patch calls GetCenturyRtcAddress() in entry point to fix
the bug.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ruiyu Ni <ruiyu.ni@intel.com>
Cc: Anbazhagan Baraneedharan <anbazhagan@hp.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Cc: Star Zeng <star.zeng@intel.com>