Fix precision mismatch issues in dEQP-VK.glsl

Fix precision mismatch issues in dEQP-VK.glsl

Changed tests:

dEQP-VK.glsl.functions.*
dEQP-VK.glsl.linkage.*
dEQP-VK.glsl.scoping.*
dEQP-VK.glsl.swizzles.*

Removed tests:

dEQP-VK.glsl.linkage.varying.rules.differing_precision_1
dEQP-VK.glsl.linkage.varying.rules.differing_precision_2
dEQP-VK.glsl.linkage.varying.rules.differing_precision_3

VK-GL-CTS issue: 214
Components: Vulkan

Change-Id: I48c7a5573b485340daa5be9db6aab1fbc70a6fc5