SourceLevelDebugPkg/DxeDebugAgent: Initialize Local APIC Timer early

SourceLevelDebugPkg/DxeDebugAgent: Initialize Local APIC Timer early

Now Debug Agent library uses Local APIC Timer to implement time-out mechanism.
But it does not initialize Local APIC Timer before transfer data with HOST.
This fix is to move Local APIC Timer initialization to
SetupDebugAgentEnvironment().
This fix also updates function header and fixed one typo of
SetupDebugAgentEnvironment() name.

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@17457 6f19259b-4bc3-4df7-8a09-765794883524