memory: tegra20: Support hardware versioning and clean up OPP table initialization

Support hardware versioning, which is now required for Tegra20 EMC OPP.
Clean up OPP table initialization by using a error code returned by OPP
API for judging about the OPP table presence in a device-tree and remove
OPP regulator initialization because we're now going to use power domain
instead of a raw regulator. This puts Tegra20 EMC OPP preparation on par
with the Tegra30/124 EMC drivers.

Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Acked-by: Thierry Reding <treding@nvidia.com>
Link: https://lore.kernel.org/r/20201203192439.16177-3-digetx@gmail.com


Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>