arm: Add support for ST-Ericsson U8500 SoC

The NovaThor U8500 SoC was released by ST-Ericsson in 2011.
It was used for some development boards like the CALAO Systems
Snowball SBC, but mass production was primarily for Android
smartphones like the Samsung Galaxy S III mini.

Previous support for U8500 was removed in
commit 68282f55 ("arm: Remove unused ST-Ericsson u8500 arch")
since none of the boards were converted to generic boards
before the deadline.

The new code does not have much in common with the previous code.
I have completely rewritten everything, embracing the Driver Model
and device trees wherever possible.

The U8500 support is a bit more minimal for now - my primary
use case is to use U-Boot as alternative bootloader for some of the
U8500 Samsung smartphones. At the moment U-Boot is chain-loaded from
the original Samsung bootloader. A side effect of this is that we
can (temporarily) get away without implementing some functionality
- e.g. all clocks are already enabled by the original bootloader.

More functionality will be added in future patches.

Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
Cc: John Rigby <john.rigby@linaro.org>
Signed-off-by: Stephan Gerhold <stephan@gerhold.net>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>