soc/tegra: fuse: Update the SoC revision attribute to display a name

Currently the SoC revision attribute for Tegra devices displays the
value of the enum associated with a particular revision. This is not
very useful because to obtain the actual revision you need to
use the tegra_revision enumeration to translate the value.

It is more meaningful to display a name for the revision, such as
'A01', than the enumarated value and therefore, update the revision
attribute to display a name. This change does alter the ABI, which
is unfortunate, but this is more meaningful and maintable.

Signed-off-by: Jon Hunter <jonathanh@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>