dmaengine: tegra-apb: Remove assumptions about unavailable runtime PM

The runtime PM is always available on all Tegra SoCs since the commit
40b2bb1b ("ARM: tegra: enforce PM requirement"), so there is no
need to handle the case of unavailable RPM in the code anymore.

Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Acked-by: Jon Hunter <jonathanh@nvidia.com>
Link: https://lore.kernel.org/r/20200209163356.6439-11-digetx@gmail.com


Signed-off-by: Vinod Koul <vkoul@kernel.org>