docs: add HDMI stack overflow troubleshooting for Cubie A7A

[tangzz-radxa]

Summary

Adds troubleshooting section for HDMI stack overflow issue reported in GitHub issue #1362 to the Cubie A7A Quick Start documentation.

Why

Issue #1362 reported an HDMI stack overflow error on Cubie A7A with the error message:

Unhandled Exception in EL3.
x30            = 0x00000000480002b0
x0             = 0x0000000048020a70
x1             = 0x00000000004404ff

A community member provided helpful troubleshooting steps in the issue comments, but this information wasn't documented in the official documentation. Adding this troubleshooting section will help other users who encounter the same issue.

The troubleshooting section includes:

1. Using a higher capacity SD card (32GB+ recommended)
2. Headless mode for first boot (don't connect HDMI until after initial boot)
3. Checking power supply (5V/3A or higher recommended)
4. Updating to the latest system image

Verification

1. The changes are minimal and focused on the reported issue
2. Both Chinese and English documentation are updated in sync
3. The troubleshooting steps are based on actual user experience from the GitHub issue
4. The section is added to the appropriate location in the Quick Start guide
5. No existing content is modified, only a new section is added

Fixes #1362