boards: st: stm32n6 boards: Add netif:eth twister support

Twister netif:eth was missing on stm32n6 based board and hence they
were not build against net samples.
Fix this.

Additionally, on dk, fix `pwm` to respect alphabetical order.

Signed-off-by: Erwan Gouriou <[email protected]>

Author: erwango

boards/st/nucleo_n657x0_q/twister.yaml

@@ -12,6 +12,7 @@ supported:
   - dma
   - i2c
   - gpio
+  - netif:eth
   - spi
   - uart
   - usb_device

boards/st/stm32n6570_dk/twister.yaml

@@ -14,8 +14,9 @@ supported:
   - dma
   - i2c
   - gpio
-  - pwm
   - memc
+  - netif:eth
+  - pwm
   - spi
   - uart
   - usb_device