remoteproc: qcom: wcnss: Allow specifying firmware-name

Introduce a firmware-name property, in order to be able to support
device/platform specific firmware for the wireless connectivity
subsystem; in line with other Qualcomm remoteproc drivers.

Link: https://lore.kernel.org/r/20200108055252.639791-1-bjorn.andersson@linaro.org


Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>