remoteproc: mediatek: Allow reading firmware-name from DT

remoteproc: mediatek: Allow reading firmware-name from DT

The SCP firmware blob differs between platforms and SoCs. We add
support in the SCP driver for reading the path of firmware file from
DT in order to allow these files to live in a generic file system
(or linux-firmware).

The firmware-name property is optional and the code falls back to the
old filename if the property isn't present.

Signed-off-by: Allen-KH Cheng <allen-kh.cheng@mediatek.com>
Reviewed-by: Rex-BC Chen <rex-bc.chen@mediatek.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://lore.kernel.org/r/20220419123331.14377-3-allen-kh.cheng@mediatek.com
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>