power: reset: syscon-poweroff: Move device data into a struct

Currently all these device data elements are top level global variables.
Move these into a struct. This will be used in the next patch when
the global variable usage is removed. Doing this in two steps makes
the patches easier to read.

Signed-off-by: Andrew Davis <afd@ti.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://lore.kernel.org/r/20240212162831.67838-19-afd@ti.com


Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>