intel/compiler: fix derivative on y axis implementation

intel/compiler: fix derivative on y axis implementation

This rewrites the ddy in EXECUTE_4 mode with a loop to make it more
obvious what is going on and also sets the group each of the 4 threads
in the groups are supposed to execute.

Fixes the following CTS tests :

   dEQP-VK.glsl.derivate.dfdyfine.dynamic_*

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Co-Authored-by: Jason Ekstrand <jason@jlekstrand.net>
Reviewed-by: Matt Turner <mattst88@gmail.com>
Fixes: 2134ea380033d5 ("intel/compiler/fs: Implement ddy without using align16 for Gen11+")