drivers: sdhc: imx_usdhc: assume card is present if no detection method

The imx USDHC driver previously queried the peripheral's internal card
detect signal to check card presence if no card detect method was
configured. However, some boards do not route the card detect signal and
do not work correctly with the DAT3 detection method supported by this
peripheral. As a fallback, assume the card is present in the slot but
log a warning to the user.

Fixes #42227

Signed-off-by: Daniel DeGrasse <daniel.degrasse@nxp.com>
(cherry picked from commit 17f71e19)