Add function to get chip revision, and print it out at boot time.

Restructure the fuse access to just use cached variables instead
of always reading the fuses, and export those variables directly
instead of using accessor functions.

Add a SKU ID table of currently known values.

Based on code originally by Colin Cross <ccross@android.com>.

Changes since v1:

* Add A01 minor rev support
* Don't decode for A03p on anything but T2x
Signed-off-by: Olof Johansson <olof@lixom.net>
Acked-by: Stephen Warren <swarren@nvidia.com>