reset: mchp: sparx5: Map cpu-syscon locally in case of LAN966x

In the LAN966x PCI device use case, the syscon API cannot be used as
it does not support device removal [1]. A syscon device is a core
"system" device and not a device available in some addon boards and so,
it is not supposed to be removed. The syscon API follows this assumption
but this assumption is no longer valid in the LAN966x use case.

In order to avoid the use of the syscon API and so, support for removal,
use a local mapping of the syscon device.

Link: https://lore.kernel.org/all/20240923100741.11277439@bootlin.com/

 [1]
Signed-off-by: Herve Codina <herve.codina@bootlin.com>
Reviewed-by: Steen Hegelund <Steen.Hegelund@microchip.com>
Reviewed-by: Philipp Zabel <p.zabel@pengutronix.de>
Link: https://lore.kernel.org/r/20241014124636.24221-4-herve.codina@bootlin.com


Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>