Add support for generic BCM SoC chipsets

In order to start upstreaming Broadcom SoC support, create
a starting hierarchy, arch and dts files.
The first support SoC family that is planned is the
BCM281XX (BCM11130/11140/11351/28145/28155) family of dual A9 mobile
SoC cores.
This code is just the skeleton code for get the machine upstreamed. It
has been made MULTIPLATFORM compatible.
Next steps
----------
Upstream a basic set of drivers - sufficient for a console boot to
ramdisk. These will includer timer, gpio, i2c drivers.
After this basic set, we will proceed with a more comprehensive set
of drivers for the 281XX SoC family.

v2 patch mods
--------
 - Remove l2x0_of_init call as there were problems with the code.
   A separate patch will be submitted with cache init code
 - Rename capri files and refs to bcm281xx-based names
 - Add bcm281xx binding doc
 - various misc cleanups

v3 patch mods
-------------
 - Remove extra #include lines
 - Remove remaining references to capri
 - dt uart chipset string added
 - cleaned up chip # references

v4 patch mods
-------------
 - swap order of compatible definitions for uart
 - fix typo

v5 patch mods
-------------
 - Rename bcm281xx to bcm11351 in dts+code,
   leaving references to bcm281xx only in help+comments.

v6 patch mods
-------------
 - fix typo in uart 'compatible' string

Signed-off-by: Christian Daudt <csd@broadcom.com>
Reviewed-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Olof Johansson <olof@lixom.net>