mfd: bd718x7: Remove hardcoded config for button press duration

The reset button on imx8mm-evk is tied to PWRON_B pin of bd71847 and the
long press duration is set to zero from OTP. The linux driver overrides
those values and breaks reset from button.

Overwriting OTP or bootloader configuration with some hardcoded defaults
is not desirable, keep already programmed values instead.

Signed-off-by: Leonard Crestez <leonard.crestez@nxp.com>
Acked-By: Matti Vaittinen <matti.vaittinen@fi.rohmeurope.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>