Avoid out-of-range depth values

Avoid out-of-range depth values

The "d32_sfloat_large_depth" variants of the
dEQP-VK.glsl.builtin_var.fragdepth.* tests rely on undefined behavior
because it uses an out-of-range depth value. The unextended Vulkan spec
requires depth values to be in the range of 0.0..1.0. The test was using
a depth value of 20.0..21.0 and expecting the implementation to clamp.

Instead of disabling this part of the test entirely, only run it if the
implementation exposes the VK_EXT_depth_range_unrestricted device
extension, which does have defined behavior with depth values outside
the range of 0.0..1.0.

Affects:

dEQP-VK.glsl.builtin_var.fragdepth.*d32_sfloat_large_depth

Components: Vulkan

VK-GL-CTS issue: 623

Change-Id: I436b8b98bebe3ef37bd306d93da2bf8c40eee6c8