Device groups can be used to:
- only render on certain physical devices, using a device mask
- only allocate memory on certain physical devices, using a
  device mask
- distribute rendering across different physical devices,
  using different render areas for each physical device

SwiftShader only supports a single physical device, so most of
these settings can simply be ignored.

Bug b/117974925

Change-Id: Ic61e1551e3a54671f8780cb7bec5c67aaa37ec09
Tests: dEQP-VK.device_group.*
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/30790
Presubmit-Ready: Alexis Hétu <sugoi@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Tested-by: Alexis Hétu <sugoi@google.com>