Add tests to use OpPhi with various variable types

Add tests to use OpPhi with various variable types

Based on the spec, OpPhi should be able to handle any variable type.
These tests use various variable types (int, float, vec3, mat4, array
and struct) with the OpPhi instruction.

All of the tests are of the form:

    testtype r

    if (indata > 0)
        r = 1
    else
        r = -1

    return (float)r

Affects:

dEQP-VK.spirv_assembly.instruction.compute.opphi.vartype_int
dEQP-VK.spirv_assembly.instruction.compute.opphi.vartype_float
dEQP-VK.spirv_assembly.instruction.compute.opphi.vartype_vec3
dEQP-VK.spirv_assembly.instruction.compute.opphi.vartype_mat4
dEQP-VK.spirv_assembly.instruction.compute.opphi.vartype_array
dEQP-VK.spirv_assembly.instruction.compute.opphi.vartype_struct

Components: Vulkan

VK-GL-CTS issue: 259

Change-Id: I2d090d06c52c904d66b35f8cee5f2895a2087069