iommu/exynos: Always enable runtime PM

Checking if the probing device has a parent device was just to discover
if the probing device is involved in a power domain when the power
domain controlled by Samsung's custom implementation.
Since generic IO power domain is applied, it is required to remove
the condition to see if the probing device has a parent device.

Signed-off-by: Cho KyongHo <pullip.cho@samsung.com>
Signed-off-by: Shaik Ameer Basha <shaik.ameer@samsung.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>