soc/tegra: fuse: Cache values of straps and Chip ID registers

There is no need to re-read Chip ID and HW straps out from hardware each
time, it is a bit nicer to cache the values in memory.

Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>