iommu/rockchip: Use iopoll helpers to wait for hardware

This patch converts the rockchip-iommu driver to use the in-kernel
iopoll helpers to wait for certain status bits to change in registers
instead of an open-coded custom macro.

Signed-off-by: Tomasz Figa <tfiga@chromium.org>
Signed-off-by: Jeffy Chen <jeffy.chen@rock-chips.com>
Reviewed-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>