ARM: tegra: apbio access using dma for tegra20 only

The Tegra20 HW issue with accessing APBIO registers (such
as fuse registers) directly from the CPU concurrently with
APB DMA accesses has been fixed in Tegra30 and later chips.

Access these registers directly from the CPU on Tegra30
and later, and apply the workaround only for Tegra20.

Signed-off-by: Laxman Dewangan <ldewangan@nvidia.com>
Tested-by: Chaitanya Bandi <bandik@nvidia.com>
Signed-off-by: Stephen Warren <swarren@nvidia.com>