samples: disable usermode for ip_k66f

in ip_k66f platfrom, we using rtt as debug port,
which is conflicted with usermode. see below:

warning: LOG_PRINTK
 (defined at subsys/logging/Kconfig.processing:8)
 has direct dependencies !USERSPACE && !LOG_MODE_MINIMAL
 && LOG with value n, but is currently being y-selected
 by the following symbols:
 - LOG_BACKEND_RTT_FORCE_PRINTK
   (defined at subsys/logging/backends/Kconfig.rtt:103),
   with value y, direct dependencies LOG_BACKEND_RTT &&
   !LOG_FRONTEND_ONLY && !LOG_MODE_MINIMAL && LOG (value: y),
   and select condition LOG_BACKEND_RTT &&
   !LOG_FRONTEND_ONLY && !LOG_MODE_MINIMAL && LOG (value: y)

Signed-off-by: Hake Huang <hake.huang@oss.nxp.com>