irqchip: bcm7120-l2: Extend driver to support 64+ bit controllers

Most implementations of the bcm7120-l2 controller only have a single
32-bit enable word + 32-bit status word.  But some instances have added
more enable/status pairs in order to support 64+ IRQs (which are all
ORed into one parent IRQ input).  Make the following changes to allow
the driver to support this:

 - Extend DT bindings so that multiple words can be specified for the
   reg property, various masks, etc.

 - Add loops to the probe/handle functions to deal with each word
   separately

 - Allocate 1 generic-chip for every 32 IRQs, so we can still use the
   clr/set helper functions

 - Update the documentation

This uses one domain per bcm7120-l2 DT node.  If the DT node defines
multiple enable/status pairs (i.e. >=64 IRQs) then the driver will
create a single IRQ domain with 2+ generic chips.  Multiple generic chips
are required because the generic-chip code can only handle one
enable/status register pair per instance.

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lkml.kernel.org/r/1415342669-30640-12-git-send-email-cernekee@gmail.com


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