"hidden_dynamic_lds_size" argument will be added in the reserved section
at offset 120 of the implicit argument layout.
Add "isDynamicLDSUsed" flag to AMDGPUMachineFunction to identify if a
function uses dynamic LDS.
hidden argument will be added in below cases:
- LDS global is used in the kernel.
- Kernel calls a function which uses LDS global.
- LDS pointer is passed as argument to kernel itself.