Tegra2 hangs if APB registers are accessed from the cpu during an
apb dma operation. The workaround is to use apb dma to read/write the
registers instead.

There is a dependency loop between fuses, clocks, and APBDMA.  If dma
is enabled, fuse reads must go through APBDMA to avoid corruption due
to a hw bug.  APBDMA requires a clock to be enabled.  Clocks must read
a fuse to determine allowable cpu frequencies.

Separate out the fuse DMA initialization, and allow the fuse read
and write functions to be called without using DMA before the DMA
initialization has been completed.  Access to the fuses before APBDMA
is initialized won't hit the hardware bug because nothing else can be
using DMA.

Original fuse registar access code from Varun Wadekar
<vwadekar@nvidia.com>, improved by Colin Cross <ccross@android.com>
and later moved to separate driver by Jon Mayo <jmayo@nvidia.com>.

Major refactoring/cleanup by Olof Johansson <olof@lixom.net>.

Changes since v1:

* fix 'return false' on error condition
* dequeue dma ops in case of timeout

From: Jon Mayo <jmayo@nvidia.com>.
Signed-off-by: Jon Mayo <jmayo@nvidia.com>.
Signed-off-by: Olof Johansson <olof@lixom.net>
Acked-by: Stephen Warren <swarren@nvidia.com>