dt-bindings: arm: nvidia,tegra20-pmc: Move fixed string property names under 'properties'

Fixed string property names should be under 'properties' rather than
'patternProperties'. Additionally, without beginning and end of line
anchors, any prefix or suffix is allowed on the specified property names.

As all the nvidia,tegra20-pmc powergates child node properties are fixed
strings, change 'patternProperties' to 'properties'.

Signed-off-by: Rob Herring <robh@kernel.org>
Acked-by: Thierry Reding <treding@nvidia.com>
Link: https://lore.kernel.org/r/20220706212034.568861-1-robh@kernel.org