ARM: 7369/1: amba: add functions to add devices dynamically

Add two functions to add APB and AHB devices to the amba (PrimeCell)
bus dynamically. This is modeled after the static definition
macros recently introduced into <linux/amba/bus.h> and can
help us in factoring out a bunch of code across the kernel.
Since a lot of call sites seem to be using a returned struct
amba device* pointer, let's use that.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>