soc: qcom: wcnss_ctrl: Allow reading firmware-name from DT

The WLAN NV firmware blob differs between platforms, and possibly
devices, so add support in the wcnss_ctrl driver for reading the path of
this file from DT in order to allow these files to live in a generic
file system (or linux-firmware).

The new property is optional and the code falls back to the old filename
if the property isn't specified.

Tested-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Tested-by: Aníbal Limón <anibal.limon@linaro.org>
Link: https://lore.kernel.org/r/20210312003318.3273536-5-bjorn.andersson@linaro.org


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