remoteproc: Introduce rproc_of_parse_firmware() helper

Add a new helper function rproc_of_parse_firmware() to the remoteproc
core that can be used by various remoteproc drivers to look up the
the "firmware-name" property from a rproc device node. This property
is already being used by multiple drivers, so this helper can avoid
repeating equivalent code in remoteproc drivers.

Signed-off-by: Suman Anna <s-anna@ti.com>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Reviewed-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Link: https://lore.kernel.org/r/20200721223617.20312-3-s-anna@ti.com


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