ARM: zx: add basic support for ZTE ZX296702

Add basic code for ZTE ZX296702 platform.

[arnd: removed unused zx296702_init_machine function, and changed
       l2c aux val to default]

Signed-off-by: Jun Nie <jun.nie@linaro.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>