Float controls: graphics: fix 16bit storage validation

Float controls: graphics: fix 16bit storage validation

For graphics shaders:

Add Float16 capability and shaderFloat16 when the test case uses
16bit float in a way not supported by the 16bit storage extension.

If not using the Float16 capability, drop definitions of 16bit
constants.

Components: Vulkan

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

VK-GL-CTS issue: 1874

Change-Id: I1e25a706e0667a45b3e5b0a6c496c77feac90465
(cherry picked from commit d081b36582101f53e08fe9f3c6219013e82765e6)