net: dsa: qca8k: add CONFIG_LEDS_TRIGGERS dependency

Without LED triggers, the driver now fails to build:

drivers/net/dsa/qca/qca8k-leds.c: In function 'qca8k_parse_port_leds':
drivers/net/dsa/qca/qca8k-leds.c:403:31: error: 'struct led_classdev' has no member named 'hw_control_is_supported'
  403 |                 port_led->cdev.hw_control_is_supported = qca8k_cled_hw_control_is_supported;
      |                               ^

There is a mix of 'depends on' and 'select' for LEDS_TRIGGERS, so it's
not clear what we should use here, but in general using 'depends on'
causes fewer problems, so use that.

Fixes: e0256648

 ("net: dsa: qca8k: implement hw_control ops")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: David S. Miller <davem@davemloft.net>