feat(qemu): add A76/N1 cpu support for virt

Add support to "cortex-a76" and "neoverse-n1" cpu for "qemu" ('virt')
platform.

Signed-off-by: Chen Baozi <chenbaozi@phytium.com.cn>
Change-Id: I77a3e0bb8397a2fb45a2caa7d93ba38e39297f93