Add feature badges to preemphasis and deemphasis functions (#2892)

Summary:
Adds feature badges to preemphasis and deemphasis functions

Pull Request resolved: https://github.com/pytorch/audio/pull/2892

Reviewed By: carolineechen

Differential Revision: D41830782

Pulled By: hwangjeff

fbshipit-source-id: 487ce9afa8dc8fe321aa9e02cc88bb1453985d39

torchaudio/prototype/functional/functional.py

@@ -354,6 +354,10 @@ def preemphasis(waveform, coeff: float = 0.97) -> torch.Tensor:
     .. math::
         y[i] = x[i] - \text{coeff} \cdot x[i - 1]
 
+    .. devices:: CPU CUDA
+
+    .. properties:: Autograd TorchScript
+
     Args:
         waveform (torch.Tensor): Waveform, with shape `(..., N)`.
         coeff (float, optional): Pre-emphasis coefficient. Typically between 0.0 and 1.0.
@@ -375,6 +379,10 @@ def deemphasis(waveform, coeff: float = 0.97) -> torch.Tensor:
     .. math::
         y[i] = x[i] + \text{coeff} \cdot y[i - 1]
 
+    .. devices:: CPU CUDA
+
+    .. properties:: Autograd TorchScript
+
     Args:
         waveform (torch.Tensor): Waveform, with shape `(..., N)`.
         coeff (float, optional): De-emphasis coefficient. Typically between 0.0 and 1.0.