arm64: Add mmio_addr arg to arm/micro-bench

Add a command line arg to arm/micro-bench to set the mmio_addr to other
values besides the default QEMU one. Default to the QEMU value if no arg
is passed.

Signed-off-by: Ricardo Koller <ricarkol@google.com>
Message-Id: <20211008174022.3028983-1-ricarkol@google.com>
Signed-off-by: Andrew Jones <drjones@redhat.com>