soc: rockchip: power-domain: avoid infinite loop

In some cases, we have met the infinite loop in
rockchip_pmu_set_idle_request() or rockchip_do_pmu_set_power_domain().

As the crosbug.com/p/57351 reported, the boot hangs right after this
[1.629163] bootconsole [uart8250] disabled
[1.639286] [drm:drm_core_init] Initialized drm 1.1.0 20060810
[1.645926] [drm:drm_get_platform_dev] Initialized vgem 1.0.0 20120112..
[1.654558] iommu: Adding device ff8f0000.vop to group 0
[1.660569] iommu: Adding device ff900000.vop to group 1
<hang>

This patch adds the error message and timeout to avoid infinite loop if
it fails to get the ack.

Signed-off-by: Caesar Wang <wxt@rock-chips.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>