Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
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+.. SPDX-License-Identifier: GPL-2.0
+
+===========================
+MIPS-specific Documentation
+===========================
+
+.. toctree::
+   :maxdepth: 2
+   :numbered:
+
+   ingenic-tcu
+
+   au1xxx_ide
+
+.. only::  subproject and html
+
+   Indices
+   =======
+
+   * :ref:`genindex`