samples: usb: dfu: Exclude Atmel SAM

The dfu sample filter seems not to work. It should select only boards
when slot0_partition and slot1_partition are define.

filter:
    dt_label_with_parent_compat_enabled("slot0_partition",
					"fixed-partitions")
and dt_label_with_parent_compat_enabled("slot1_partition",
					"fixed-partitions")
and dt_chosen_enabled("zephyr,flash-controller")
and CONFIG_FLASH_HAS_DRIVER_ENABLED

This means that sam4l_ek, same54_xpro and samr21_xpro should never be
selected because the final devicetree is defined without those
partitions. See below fragment from same54_xpro:

nvmctrl: nvmctrl@41004000 {
	compatible = "atmel,sam0-nvmctrl";
	reg = < 0x41004000 0x22 >;
	interrupts = < 0x1d 0x0 >, < 0x1e 0x0 >;
	#address-cells = < 0x1 >;
	#size-cells = < 0x1 >;
	lock-regions = < 0x20 >;
	flash0: flash@0 {
		compatible = "soc-nv-flash";
		write-block-size = < 0x8 >;
		reg = < 0x0 0x100000 >;
		partitions {
			compatible = "fixed-partitions";
			#address-cells = < 0x1 >;
			#size-cells = < 0x1 >;
			storage_partition: partition@fc000 {
				label = "storage";
				reg = < 0xfc000 0x4000 >;
			};
		};
	};
};

This excludes same54_xpro and samr21_xpro to avoid ci issues until ci
filter is fixed.

Signed-off-by: Gerson Fernando Budke <nandojve@gmail.com>