dts: bindings: Fix license identifiers in a few files provided by Nordic

Correct license identifiers in two files copied from internal Nordic
repositories that were not properly adjusted for Zephyr:
- dts/bindings/flash_controller/nordic,rram-controller.yaml (added in
  commit 3a8ee7df)
- dts/bindings/misc/nordic,nrf-dppic-local.yaml (added in commit
  796d09d2)

Signed-off-by: Andrzej Głąbek <andrzej.glabek@nordicsemi.no>