ARM: sunxi: mc-smp: Split out SoC-specific device node lookup sequence

The multi-cluster SMP code maps the address spaces of several hardware
control blocks. The device nodes for them are SoC-specific. To help with
supporting other SoCs to re-use this code, these bits should be split
out to a separate function tied to the enable-method string.

This patch splits out and groups the device node lookup sequence, and
adds new data structures to have the newly created function tied to
the enable method string. This structure can also be used to encode
other differences between the SoCs.

Acked-by: Maxime Ripard <maxime.ripard@bootlin.com>
Signed-off-by: Chen-Yu Tsai <wens@csie.org>