UefiCpuPkg: Setting initial-count register as the last step

UefiCpuPkg: Setting initial-count register as the last step

BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=3711

Per SDM, changing the mode of APIC timer (from one-shot to periodic or
vice versa) by writing to the timer LVT entry does not start the timer.
To start the timer, it is necessary to write to the initial-count
register.

If initial-count is wrote before mode change, it's possible that timer
expired before the mode change. Thus failing the periodic mode.

Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: Anthony Perard <anthony.perard@citrix.com>
Cc: Julien Grall <julien@xen.org>
Cc: Eric Dong <eric.dong@intel.com>
Cc: Ray Ni <ray.ni@intel.com>
Acked-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Ray Ni <ray.ni@intel.com>
Reviewed-by: Jiewen Yao <jiewen.yao@intel.com>
Signed-off-by: Min Xu <min.m.xu@intel.com>