power: bq24257: Remove IRQ config through stat-gpios

At the time the driver was written GpioInt resources in ACPI were not
passed to the driver in client->irq, as opposed to DT enumeration. To
accommodate this use case, a "stat-gpios" property was introduced to
allow configuring the IRQ.

However this issue with ACPI was fixed in commit "845c8770 i2c / ACPI:
Assign IRQ for devices that have GpioInt automatically" and makes this
workaround no longer necessary, hence we can remove the support for the
"stat-gpios" property and the associated code from the bq24257 driver.

Signed-off-by: Andreas Dannenberg <dannenberg@ti.com>
Signed-off-by: Sebastian Reichel <sre@kernel.org>