Properly align and pad vec16x2 values in UBO array

Properly align and pad vec16x2 values in UBO array

Each of vec16x2 element should be thightly packed, followed by padding.

Without this change the test was padding each float16 value.

Components: Vulkan

VK-GL-CTS Issue: 1436

Affects:
	dEQP-VK.spirv_assembly.instruction.compute.16bit_storage.uniform_16_to_64.uniform_vector_float
	dEQP-VK.spirv_assembly.instruction.graphics.16bit_storage.uniform_float_16_to_64.uniform_vector_float*

Change-Id: I4405a96eb5a27cfd8bf362853b28d59f20cb2314
(cherry picked from commit 8dbff9d866aa838047c641a5eeab19381be3df4f)