UefiCpuPkg/MpInitLib: fix issue in wakeup buffer initialization

UefiCpuPkg/MpInitLib: fix issue in wakeup buffer initialization

To fix an issue in which enabling NX feature will mark the AP wakeup
buffer as non-executable and fail the AP init, the buffer was split
into two part: the lower part in memory within 1MB and the higher part
within allocated executable memory (EfiBootServicesCode). But the
address of higher part memory was stored in lower part memory, which
is actually shared with legacy components and will be overwritten by
LegacyBiosDxe driver if CSM is enabled.

This patch fixes this issue by storing the address of higher part
memory in CpuMpData instead of ExchangeInfo.

Cc: Ruiyu Ni <ruiyu.ni@intel.com>
Cc: Eric Dong <eric.dong@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Jian J Wang <jian.j.wang@intel.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>