SourceLevelDebugPkg/DebugAgentDxe: Move help info from DxeDebugAgent

SourceLevelDebugPkg/DebugAgentDxe: Move help info from DxeDebugAgent

Now DxeDebugAgent Library instance will print help information on how to load
DebugAgentDxe.efi in UEFI shell. But it is printed after Target connected to
Host side. This fix is to move help info print to DebugAgentDxe module before
Target tries to connect HOST. It could help developer to get useful information
as early as possible.

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@17458 6f19259b-4bc3-4df7-8a09-765794883524