Fix SWM init retry when SRE is not ready

[mikitl]

Description

GopRegisteredCallback sets mGop when it finds GOP but exits early if SRE is not available yet. Because mGop remains set, the callback never retries on subsequent GOP notifications, so SWM never initializes.

Reset mGop to NULL when SRE is not found so the callback can retry.

• Impacts functionality?
• Impacts security?
• Breaking change?
• Includes tests?
• Includes documentation?

How This Was Tested

Tested on:

• ARM64 platform with GPU driver that installs GOP during early display enumeration, before GopOverrideDxe and SRE have processed it
• Verified SWM callback retries and completes Stage2 initialization after SRE becomes available
• Confirmed Front Page and on-screen keyboard render correctly
• Verified no regression when GOP and SRE appear simultaneously (standard boot path)

Integration Instructions

N/A

[mu-automation]

✅ QEMU Validation Passed

Source Dependencies

Repository	Commit
mu_plus	3a492ef
mu_tiano_platforms	78fad16

Results

Platform	Target	Build	Boot	Overall Boot Time	Build Logs	Boot Logs
Q35	DEBUG	✅ success	✅ success	0m 17s	Build Logs	Boot Logs
SBSA	DEBUG	✅ success	✅ success	0m 33s	Build Logs	Boot Logs

Workflow run: https://github.com/microsoft/mu_plus/actions/runs/25746719364

This comment was automatically generated by the Mu QEMU PR Validation workflow.