docs: Fix typo in Documentation/x86/x86_64/5level-paging.rst

fix two typos in the documentation
(Documentation/x86/x86_64/5level-paging.rst), changing 'paing' for 'paging'
and using the right verbal form for plural on 'some vendors offer'.

Signed-off-by: Carlos Bilbao <bilbao@vt.edu>
Link: https://lore.kernel.org/r/2599991.mvXUDI8C0e@iron-maiden
Signed-off-by: Jonathan Corbet <corbet@lwn.net>