irqchip: bcm7120-l2: Decouple driver from brcmstb-l2

Some chips, such as BCM6328, only require bcm7120-l2.  Some BCM7xxx STB
configurations only require brcmstb-l2.  Treat them as two separate
entities, and update the mach-bcm dependencies to reflect the change.

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Link: https://lkml.kernel.org/r/1415342669-30640-13-git-send-email-cernekee@gmail.com


Signed-off-by: Jason Cooper <jason@lakedaemon.net>