There is an issue related to the HSUART DMA support in the kernel that will hang on reboot or shutdown. To prevent this, add those lines to /etc/modprobe.d/blacklist.conf:
blacklist dw_dmac_core
install dw_dmac /bin/true
install dw_dmac_core /bin/true
Then, update initramfs:
sudo update-initramfs -u