ARM: tegra: export apb dma readl/writel

ARM: tegra: export apb dma readl/writel

Export APB DMA readl and writel. These are needed because we can't access
the fuses directly on Tegra20 without potentially causing a system hang.
Also have the APB DMA readl and writel return an error in case of a read
failure instead of just returning zero or ignore write failures.

Signed-off-by: Peter De Schrijver <pdeschrijver@nvidia.com>
Signed-off-by: Stephen Warren <swarren@nvidia.com>