doc: sphinx-lint: fix bad usage of "default role"

Fixes bad usage of single backticks in lieu of double backticks for
rendering inline literals, or simple '*' for italics.

When appropriate, a better construct than double backticks has been
selected (ex. :file:, :kconfig:option:, :c:func:, ...), or proper :ref:
have been used if the original intention was to have a link.

Signed-off-by: Benjamin Cabé <benjamin@zephyrproject.org>