dt-bindings: firmware: tegra186-bpmp: Remove name property

This property is not used by device trees and was likely supposed to be
a hint as to what the BPMP node should be named, rather than describing
a property of the BPMP node.

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