dt-bindings: arm: Add the actual power domains on U8500

This file has been left in an unfinished state just defining
the root power domain for the U8500 SoC. Fix it up by adding
the actual existing power domains in this SoC.

The PRCMU code and old regulator driver is mentioning some
*_RET domains, this means "retention" and is a state in the
domain and not a domain of its own.

Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@oss.qualcomm.com>
Signed-off-by: Linus Walleij <linusw@kernel.org>
Signed-off-by: Ulf Hansson <ulfh@kernel.org>