This function can only handle a syscon device. It is possible that someone
will make a mistake, so add a check for this.
Also we should return -ENODEV when a device cannot be found, so update the
syscon_get_regmap_by_driver_data() to follow this convention.
Signed-off-by: Simon Glass <sjg@chromium.org>
Many SoCs have a number of system controllers which are dealt with as a
group by a single driver. It is a pain to have to add lots of compatible
strings and/or separate drivers for each. Instead we can identify the
controllers by a number and request the address of the one we want.
Add a simple implementation of this which can be used by SoC driver code.
Signed-off-by: Simon Glass <sjg@chromium.org>