[site] Restrict toc to longer pages
[site] Restrict toc to longer pages

Do not print the table of contents on short pages.

This is also a small hack to not have the table of contents on pages
which only have references to other pages and where is make not much
sense to have the overview.

Signed-off-by: Tobias Wölfel <5d52ef3ca07cd47a5b2415323e8983bd6b99d040@mailbox.org>

lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan