ata: libahci: Use of_platform_device_create only if supported

of_platform_device_create does not exist if OF_ADDRESS is not configured,
so limit its use accordingly.

Without this fix, the sparc64:allmodconfig build fails with

ERROR: "of_platform_device_create" [drivers/ata/libahci_platform.ko] undefined!

Fixes: c7d7ddee ("ata: libahci: Allow using multiple regulators")
Cc: Gregory CLEMENT <gregory.clement@free-electrons.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Tejun Heo <tj@kernel.org>