mfd: ab8500-core: Add device tree support for AB8505

AB8505 support was never fully converted to the device tree.
Most of the MFD cells for AB8505 lack an "of_compatible",
which prevents them from being configured through the device tree.

Align the definition of the AB8505 MFD cells with the ones for AB8500,
and add device tree compatibles. Except for GPIO and regulators the
compatibles are equal to those used for AB8500 because the hardware
does not differ much.

Finally, change db8500_prcmu_register_ab8500() to check for the AB8505
device tree node additionally, and probe it if it is found.

Signed-off-by: Stephan Gerhold <stephan@gerhold.net>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>