arm64: tegra: Assume no CLKREQ presence by default

Although Tegra194 has support for CLKREQ sideband signal and P2972
has routing of the same till the slot, it is the case most of the time
that the connected device doesn't have CLKREQ support. Hence, it makes
sense to assume that there is no CLKREQ support by default and it can
be enabled on need basis when a card with CLKREQ support is connected.

Signed-off-by: Vidya Sagar <vidyas@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>