DfciPkg: make manager + settings drivers dispatch-order resilient

[kat-perez]

Description

Makes DfciManager work under any DXE dispatcher that ignores [Depex], without changing observable behavior under EDK2 BdsDxe:

• Replace the three entry-time LocateProtocol calls for gDfciApply*ProtocolGuid (Identity, Permissions, Settings) with RegisterProtocolNotify. Each callback populates its static when the producer installs; when all three are present, a new DfciManagerCompleteInit() runs the original sequence (AllocateManagerData → EndOfDxe callback → QueueMailboxAtSettingAccess).

• Under EDK2 + [Depex], producers are already present when this driver dispatches, so all three notifies fire synchronously on registration and CompleteInit runs before entry returns — byte-identical observable behavior.

• Under a dispatcher that ignores [Depex], CompleteInit runs whenever the producers actually arrive.

Also fixes two latent NULL derefs that become reachable when ProcessMailBoxes is re-entered after FreeManagerData() has cleared state (e.g. if a duplicate gDfciSettingAccessProtocolGuid notify registration causes the callback to fire twice):

• Top-of-ProcessMailBoxes early-exit when mManagerData[MGR_IDENTITY].Data is NULL.
• Split the existing combined if (Data == NULL || Data->Packet == NULL) in ProcessPacket so the Data == NULL branch doesn't reach the Data->MailboxName dereference inside its DEBUG message.

[Depex] entries are left intact — belt-and-suspenders under EDK2, harmless elsewhere.

• Impacts functionality?
• Impacts security? (NULL-deref hardening in a privileged driver)
• Breaking change?
• Includes tests?
• Includes documentation?

How This Was Tested

Built Msft900MaaPkg (DEBUG + RELEASE) under standard EDK2 BdsDxe and verified normal boot through bootmgfw.efi is byte-equivalent to the pre-change firmware. Override-hash validation against a downstream SEMM consumer (which uses DfciManager's [Sources] as its #Override baseline) passes after a one-line hash refresh on the consumer's .inf.

The ProcessMailBoxes re-entry NULL-deref was originally observed on a non-EDK2 dispatcher that registered duplicate gDfciSettingAccessProtocolGuid notifies — the top-of-function guard makes the second invocation safe regardless of dispatcher.

Integration Instructions

N/A — backward compatible with all existing EDK2 BdsDxe consumers.

Note: SettingsManagerDxe's gDfciStartOfBdsNotifyGuid trigger is intentionally left unchanged. Earlier iterations of this work tried moving it to gEfiEndOfDxeEventGroupGuid for universality, but that introduces re-entrant notify dispatch during EndOfDxe that the standard MdeModulePkg/Core/Dxe/DxeMain notify iterator does not survive (downstream consumers like SEMM that CloseEvent from inside the callback corrupt the iterator). Alternate dispatchers that need gDfciSettingAccessProtocolGuid publication should signal gDfciStartOfBdsNotifyGuid explicitly from their own BDS phase after EndOfDxe completes.

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