doc: qemu: arm: Add a section on booting Linux distros

Add an example qemu-system-aarch64 command that can make U-Boot on QEMU
boot into the Debian Installer, along with resulting console messages
from U-Boot, based on the existing documentation section for the x86
version.

Signed-off-by: Alper Nebi Yasak <alpernebiyasak@gmail.com>