boards: nxp: vmu_rt1170: fix SD card pin control setup

Fix SD card pinctrl setup for the VMU RT1170 board. The following
changes were made:
- use the "cd-gpios" property over detecting the card using the
  USDHC card detect register. This should be more reliable.
- bias the clk pin high. This matches setup for the RT1170 EVK SD
  pinctrl.
- remove the drive strength setting for SD pins to align with the
  pinctrl settings for low speed SD mode (50 MHz) on the RT1170 EVK.

Signed-off-by: Daniel DeGrasse <daniel.degrasse@nxp.com>