Documentation generation: update kernel-doc script to latest

Update the 'kernel-doc' script to the latest version available from
https://github.com/projectacrn/acrn-kernel.

This solves the following error when generating the ACRN documentation:
"Unescaped left brace in regex is deprecated here (and will be fatal in Perl
5.32), passed through in regex; marked by <-- HERE in m/({ <-- HERE .*})/ at
scripts/kernel-doc line 2176."

Tracked-On: #1926
Signed-off-by: Geoffroy Van Cutsem <geoffroy.vancutsem@intel.com>

Author: Geoffroy Van Cutsem