reset: microchip-sparx5: allow building as a module

Set RESET_MCHP_SPARX5 as a tristate and add MODULE_DEVICE_TABLE() to
allow building this driver as a module.

Signed-off-by: Clément Léger <clement.leger@bootlin.com>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Link: https://lore.kernel.org/r/20220617103730.490588-1-clement.leger@bootlin.com