reset: th1520: Prepare for supporting multiple controllers

reset: th1520: Prepare for supporting multiple controllers

TH1520 SoC is divided into several subsystems, shipping distinct reset
controllers with similar control logic. Let's make reset signal mapping
a data structure specific to one compatible to prepare for introduction
of more reset controllers in the future.

Signed-off-by: Yao Zi <ziyao@disroot.org>
Acked-by: Guo Ren <guoren@kernel.org>
Reviewed-by: Drew Fustini <fustini@kernel.org>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>