doc: release-notes-3.7: fix LED release notes

This patch fixes two broken links in the LED strip release note.
:kconfig:option: cannot be used with removed Kconfig options. This
results in broken links. Let's use the code's inline markup delimiter
instead.

It also adds a missing link to the DT compatible of the IS31FL3194
controller.

Signed-off-by: Simon Guinot <simon.guinot@sequanux.org>