Rename U65 & U85 device files to NPU

The U65 & U85 device files have been renamed to NPU to make it clearer
what they are for and to separate them from the direct device
implementation

Change-Id: I997b1b3d970ac7b0af8ffab6fbfd61d014eb7528
Signed-off-by: Mikael Olsson <mikael.olsson@arm.com>