dts/bindings/pinctrl: Remove usage of c comments within bindings

Reused Linux bindings were using /*  */ in some property description
fields.
This is not compatible with legacy device tree api which expands
these fields in commented sections of generated file
devicetree_legacy_unfixed.h resulting in compilation issue.
Seen when running tests/lib/devicetree/legacy_api.

Remove /* */ for now, waiting legacy api to be removed.

Signed-off-by: Erwan Gouriou <erwan.gouriou@linaro.org>