power: bq24257: Allow manual setting of input current limit

A new optional device property called "ti,current-limit" is introduced
to allow disabling the D+/D- USB signal-based charger type auto-
detection algorithm used to set the input current limit and instead to
use a fixed input current limit.

Signed-off-by: Andreas Dannenberg <dannenberg@ti.com>
Reviewed-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: Sebastian Reichel <sre@kernel.org>