i2c: cadence: Add reset controller support

The Cadence I2C controller has an external reset signal that needs to be
de-asserted before the I2C controller can be used.

Add support to the driver to be able to take the peripheral out of reset
using the reset controller API. The reset is optional in the driver for
compatibility to systems where the reset managed by the bootloader.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Acked-by: Michal Simek <michal.simek@amd.com>
Signed-off-by: Wolfram Sang <wsa@kernel.org>