UefiCpuPkg/PiSmmCpuDxeSmm: Fix failure when PcdCpuSmmDebug is TRUE

UefiCpuPkg/PiSmmCpuDxeSmm: Fix failure when PcdCpuSmmDebug is TRUE

If PcdCpuSmmDebug is set to TRUE, then the first time the function
CpuSmmDebugEntry () is called during the first normal SMI, the
registers DR6 or DR7 may be set to invalid values due to gSmst
not being fully initialized yet.  Instead, use gSmmCpuPrivate that
is fully initialized for the first SMI to look up CpuSaveState
for the currently executing CPU.

Cc: Jeff Fan <jeff.fan@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Michael Kinney <michael.d.kinney@intel.com>
Reviewed-by: Jeff Fan <jeff.fan@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@19502 6f19259b-4bc3-4df7-8a09-765794883524