Qemu ARM virtual platform emulates an ARM machine
with configurable, ARM components. This commit adds
configuration option for Cortex-A7 based virtual machine.

qemu_arm_virt_ca7 name is derived from a command
to invoke Qemu:
qemu-system-arm -M virt -cpu cortex-a7
Signed-off-by: NZbigniew Bodek <zbigniew.bodek@huawei.com>
Change-Id: Ia267ee7c989b8c22e6c19d6f11ff3ee2eef8148b