samples: fs: Extend littlefs sample to native_posix and qemu_x86

Adds native_posix and qemu_x86 the platform_allow list for the
littlefs sample application.

Signed-off-by: Dominik Ermel <[email protected]>

Author: de-nordic

samples/subsys/fs/littlefs/sample.yaml

@@ -4,5 +4,5 @@ tests:
   sample.filesystem.littlefs:
     build_only: true
     platform_allow: nrf52840dk_nrf52840 particle_xenon disco_l475_iot1
-      mimxrt1064_evk
+      mimxrt1064_evk qemu_x86 native_posix
     tags: filesystem