- Depth output should write to the 1st (Red) channel only
- Depth image load should be clamped in the [0, 1] range

Change-Id: Ic7c3ac09c86d5457ec3c59bf9666e2b168226c5e
Reviewed-on: https://swiftshader-review.googlesource.com/13988Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>