Add precision error margin to cos() tests for float_controls

Add precision error margin to cos() tests for float_controls

On some old Intel hardware, Mesa doesn't return exactly 1.0 for cos(0).
This change implements the precision error margin for the affected cos() tests,
following Vulkan spec, "Precision and Operation of SPIR-V Instructions".

Components: Vulkan

Affects: dEQP-VK.spirv_assembly.instruction.*.float_controls.*.cos_denorm_flush_to_zero*

VK-GL-CTS issue: 1498

Change-Id: I2ff07616f706d4214517917276aeb26d2d875325
Signed-off-by: Samuel Iglesias Gonsálvez <siglesias@igalia.com>