Provide a new function which can cope with obtaining information from
of-platdata instead of the device tree.

Signed-off-by: Simon Glass <sjg@chromium.org>

If the device cannot be probed, syscon_get_by_driver_data() will still
return a useful value in its devp parameter. Ensure that it returns NULL
instead.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>

We have a way to find a regmap by its syscon driver data value. Add the same
for syscon itself.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>

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>