MAINTAINERS: add maintainers for uacce

Add Zhangfei Gao and Zhou Wang as maintainers for uacce

Signed-off-by: Zhangfei Gao <zhangfei.gao@linaro.org>
Signed-off-by: Zhou Wang <wangzhou1@hisilicon.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>