Do not use hardcoded number of CUs

The code base has hardcoded values from number of CUs (or SMs) of 304 and other places where we define `gemm_sms` to be the next smaller power of 2 number (e.g., 256 When the number of CUs is 304 then comm_sms is 48). 

All these numbers need to be programmatically set (even for default argument values). Use the hip module to get the number of CUs.