dmaengine: at_xdmac: use platform_driver_register

dmaengine: at_xdmac: use platform_driver_register

When using SCMI clocks, the clocks are probed later than subsys initcall
level. This driver uses platform_driver_probe which is not compatible with
deferred probing and won't be probed again later if probe function fails
due to clocks not being available at that time.

This patch replaces the use of platform_driver_probe with
platform_driver_register which will allow probing the driver later again
when clocks will be available.

Signed-off-by: Clément Léger <clement.leger@bootlin.com>
Link: https://lore.kernel.org/r/20210728094607.50589-1-clement.leger@bootlin.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>