arch/arm64: configs: disable CONFIG_RT_GROUP_SCHED

arch/arm64: configs: disable CONFIG_RT_GROUP_SCHED

According to the Kconfig, "if enabled, it will also make it impossible
to schedule realtime tasks for non-root users until you allocate
realtime bandwidth for them."

This fixes the issue of libbluetooth unable to create timer with
SCHED_FIFO thread.

W libc    : pthread_create sched_setscheduler(1, {1}) call failed: Operation not permitted
E bt_osi_alarm: system/bt/osi/src/alarm.cc:683 timer_create_internal: timer_create_internal unable to create timer with clock 7: Operation not permitted