fix(linux): add explicit labels to U-Boot section references

As suggested by Copilot, using implicit section-title references could be broken if the referenced section changed names. Instead, explicit labels are used.

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>
Signed-off-by: Yiyoung Liu <yiyoung.md@gmail.com>

Author: maybe-yiyi

source/linux/Foundational_Components/U-Boot/BG-Target-Images-K3.rst

@@ -6,8 +6,10 @@ Target Images
 
 This page describes the boot images produced by U-Boot builds for K3-based SoCs.
 
-See the `Images`_ section for which files to copy to your SD card.
-The `Image Formats`_ section provides technical details on binary layouts for reference.
+See the :ref:`k3-images` section for which files to copy to your SD card.
+The :ref:`k3-image-formats` section provides technical details on binary layouts for reference.
+
+.. _k3-images:
 
 ******
 Images