[nrf fromtree] samples/fs/littlefs: Allow building for nrf54l15pdk

The commit adds nrf54l15pdk/nrf54l15/cpuapp target platfomr.

Signed-off-by: Dominik Ermel <[email protected]>
(cherry picked from commit e3866a9)

Author: de-nordic

samples/subsys/fs/littlefs/sample.yaml

@@ -24,6 +24,7 @@ tests:
       - stm32f746g_disco
       - stm32h747i_disco/stm32h747xx/m7
       - stm32h750b_dk
+      - nrf54l15pdk/nrf54l15/cpuapp
     integration_platforms:
       - nrf52840dk/nrf52840
   sample.filesystem.littlefs.blk: