SourceLevelDebugPkg/DebugAgent: Disable Debug Timer as early

SourceLevelDebugPkg/DebugAgent: Disable Debug Timer as early

InitializeApicTimer() will enable Local APIC timer interrupt. Even though we
disable CPU interrupt at the beginning and enable CPU Interrupt after debug
agent initialized completely, some Boot Service may invoke RestoreTpl () which
may enable CPU interrupt.
We should disable Local APIC timer in InitializeDebugTimer () to avoid Debug
Timer interrupt happens during debug port and debug agent initialization phase.
And enable Debug Timer interrupt after debug agent is initialized.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Jeff Fan <jeff.fan@intel.com>
Reviewed-by: Ruiyu Ni <ruiyu.ni@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@17572 6f19259b-4bc3-4df7-8a09-765794883524