docs: octeontx2: tune rst markup

Commit 80b94148

 ("docs: octeontx2: Add Documentation for NPA health
reporters") added new documentation with improper formatting for rst, and
caused a few new warnings for make htmldocs in octeontx2.rst:169--202.

Tune markup and formatting for better presentation in the HTML view.

Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Acked-by: George Cherian <george.cherian@marvell.com>
Link: https://lore.kernel.org/r/20210106161735.21751-1-lukas.bulwahn@gmail.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>