intel/fs: Add support for float16 to the fsign optimizations
Commit ad98fbc2 ("intel/fs: Refactor code generation for nir_op_fsign to its own function") criss-crossed with c2b8fb9a ("anv/device: expose VK_KHR_shader_float16_int8 in gen8+"), and I was not paying enough attention when I rebased. This adds back the float16 changes and enables the optimization.
Fixes: ad98fbc2 ("intel/fs: Refactor code generation for nir_op_fsign to its own function")
This is still running through the Intel CI, but it tried a couple tests locally, and it seemed okay.