dt-bindings: interrupt-controller: microchip,lan966x-oic: Clarify endpoint use

Reword the description, to make it clear that the LAN966x Outbound
Interrupt Controller is used only in PCI endpoint mode.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Acked-by: Herve Codina <herve.codina@bootlin.com>
Link: https://lore.kernel.org/all/247b1185c93610100f3f8c9e0ab2c1506e53e1f4.1737383314.git.geert+renesas@glider.be