gnu: Add linux-libre 5.11.

* gnu/packages/linux.scm (linux-libre-5.11-version, deblob-scripts-5.11,
linux-libre-5.11-pristine-source, linux-libre-5.11-source, linux-libre-5.11):
New variables.
* gnu/packages/aux-files/linux-libre/5.11-x86_64.conf,
gnu/packages/aux-files/linux-libre/5.11-i686.conf,
gnu/packages/aux-files/linux-libre/5.11-arm.conf,
gnu/packages/aux-files/linux-libre/5.11-arm64.conf: New files.
* Makefile.am (AUX_FILES): Add them.