drivers/amba: create devices from device tree

Add a function to create amba_devices (i.e. primecell peripherals)
from device tree nodes. The device tree scanning is done by the
of_platform_populate() function which can call of_amba_device_create
based on a match table entry.

Nodes with a "arm,primecell-periphid" property can override the h/w
peripheral id value.

Based on the original work by Jeremy Kerr.

Signed-off-by: Jeremy Kerr <jeremy.kerr@canonical.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Rob Herring <rob.herring@calxeda.com>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
[grant.likely: add Jeremy's original s-o-b line, changes from review
               comments, and moved all code to drivers/of/platform.c]
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>