Revert "boards/arc/qemu_arc: Disable use of branch delay slots"

This reverts commit 8084ea55.

The rootcause is fixed in the ARC QEMU which is in SDK 0.16.3.
As we've updated SDK in upstream CI we can revert this
workaround.

Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>
Signed-off-by: Evgeniy Paltsev <PaltsevEvgeniy@gmail.com>