net: fec_ptp: Use platform_get_irq_xxx_optional() to avoid error message

Use platform_get_irq_byname_optional() and platform_get_irq_optional()
instead of platform_get_irq_byname() and platform_get_irq() for optional
IRQs to avoid below error message during probe:

[    0.795803] fec 30be0000.ethernet: IRQ pps not found
[    0.800787] fec 30be0000.ethernet: IRQ index 3 not found

Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
Acked-by: Fugang Duan <fugang.duan@nxp.com>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Signed-off-by: David S. Miller <davem@davemloft.net>