scripts: west_commands: create_board: Fix nRF54LM20 FLPR DTS include

Upstream Zephyr commit 876ebb23ce16 ("dts: nordic: nrf54lm20: provide
dedicated cpuflpr dtsi") removed the SoC include from the shared
nrf54lm20_a_b_cpuflpr.dtsi, so the generated board must now include the
per-SoC nrf54lm20a_cpuflpr.dtsi or nrf54lm20b_cpuflpr.dtsi entry point
instead.

Assisted-by: Cursor:claude-opus-5
Signed-off-by: Robert Lubos <robert.lubos@nordicsemi.no>

Author: rlubos

scripts/west_commands/create_board/templates/nrf54lm/board.dts.jinja2

@@ -83,7 +83,7 @@ temp_sensor: &temp {
 {% else %}
 /dts-v1/;
 
-#include <nordic/nrf54lm20_a_b_{{ target['core'] }}.dtsi>
+#include <nordic/{{ soc }}_{{ target['core'] }}.dtsi>
 #include "{{ board }}-pinctrl.dtsi"
 
 / {