UefiCpuPkg/DxeMpLib: Allocate below 4GB mem for AsmRelocateApLoopFunc

UefiCpuPkg/DxeMpLib: Allocate below 4GB mem for AsmRelocateApLoopFunc

Current implementation just allocates reserve memory for AsmRelocateApLoopFunc.
It not be safe because APs will be placed into 32bit protected mode on long mode
DXE. This reserve memory must be located below 4GB memory.

This fix is to allocate < 4GB memory for AsmRelocateApLoopFunc.

Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Michael D Kinney <michael.d.kinney@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Jeff Fan <jeff.fan@intel.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Tested-by: Laszlo Ersek <lersek@redhat.com>
[lersek@redhat.com: strip whitespace at EOL]
Signed-off-by: Laszlo Ersek <lersek@redhat.com>