arm64: dts: qcom: apq8016-sbc: Update modem and WiFi firmware path

The firmware for the modem and WiFi subsystems platform specific and is
signed with a OEM specific key (or a test key). In order to support more
than a single device it is therefor not possible to rely on the default
path and stash these files directly in the firmware directory.

This has already been addressed for other platforms, but the APQ8016 SBC
(aka db410c) was never finished upstream.

Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Reviewed-by: Stephan Gerhold <stephan@gerhold.net>
Tested-by: Stephan Gerhold <stephan@gerhold.net>
Link: https://lore.kernel.org/r/20210531224453.783218-1-bjorn.andersson@linaro.org