x86_64: fix regression https://github.com/apache/nuttx/pull/15651

[hujun260]

Summary

x86_64: fix regression #15651

reason:
In x86_64, tcb->xcp.regs is always valid, and we obtain the location where the context is saved through irq_xcp_regs every time an interrupt occurs.

Impact

x86_64

Testing

qemu-intel64:nsh

[nuttxpr]

[Experimental Bot, please feedback here]

Yes, this PR appears to meet the basic NuttX requirements, but is lacking important details. While it identifies the problem and platform, it's missing crucial information for proper review:

• Insufficient Summary: The summary needs to explain how the regression was fixed. What was changed in the code?
• Missing Impact Details: While x86_64 is mentioned, it needs to specify whether this is a new feature, a bug fix (which it seems to be), and if there are any user-facing changes, build changes, documentation needs, etc. Even if the answer is "NO", explicitly stating it is important.
• Missing Test Logs: The provided test logs are placeholders. Actual logs demonstrating the issue before the fix and the corrected behavior after the fix are essential for verifying the change. What commands were run? What was the incorrect output? What is the correct output?
• Lack of Specificity: Phrases like "works as intended" are too vague. Be explicit about what was tested and the expected results.

In short, while the framework is there, the content needs to be significantly expanded to provide reviewers with the necessary information to properly evaluate the PR.