samples/subsys/mgmt/mcumgr/smp_svr: Limit logging from mcuboot_util
samples/subsys/mgmt/mcumgr/smp_svr: Limit logging from mcuboot_util

Fixes problem where UART DFU mage uploads via mcumgr get interrupted
by the mcuboot_util logs, causing uploads stuck and fail on time-out.

Signed-off-by: Dominik Ermel <1a1d45a9cc0c98a37f8d0a0d2dbe3cacc0b2344f@nordicsemi.no>

zephyrproject-rtos/zephyr,nashif/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,finikorg/zephyr,nashif/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,nashif/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,galak/zephyr,finikorg/zephyr,Vudentz/zephyr,Vudentz/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,Vudentz/zephyr,nashif/zephyr,galak/zephyr,Vudentz/zephyr,galak/zephyr,nashif/zephyr