gpio: vf610: update comment for i.MX8ULP and i.MX93 legacy compatibles

i.MX8ULP and i.MX93 legacy compatible strings use dual regs, while
new compatible strings use one reg. The "support old compatible strings"
is not clear to reflect the fact, so update it.

Suggested-by: Marco Felsch <m.felsch@pengutronix.de>
Signed-off-by: Peng Fan <peng.fan@nxp.com>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>