configs/microchip_sam9x60ek_mmc_dev_defconfig: add missing options

This defconfig needs wchar, thread debugging, and udev support to be
able to use all the packages it enables.

Fixes:

  https://gitlab.com/buildroot.org/buildroot/-/jobs/1478738516



Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>