docs: pdfdocs: Enable CJKspace in TOC for Korean titles

docs: pdfdocs: Enable CJKspace in TOC for Korean titles

Korean (Hangul) titles in Table of Contents of translations.pdf
don't have inter-phrase spaces.

This is because the CJKspace option of xeCJK is disabled by
default.

Restore the spaces by enabling the option at the beginning of every
document and disable it in the \kerneldocBegin{SC|TC|JP} commands.

Signed-off-by: Akira Yokosawa <akiyks@gmail.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/19141b3e-01d9-1f6d-5020-42fbda784831@gmail.com
Signed-off-by: Jonathan Corbet <corbet@lwn.net>