gpu-compute: replace uint32_t* casts with bits API calls

gpu-compute: replace uint32_t* casts with bits API calls

The uint32_t* casting was challenging to fully understand what was
being done at a glance. Replaced with calls to various bits functions
as it's functionally equivalent and much more clear.

This also fixes a segfault in GPUInitAbi DPRINTFs from a mis-typed
uint32_t* cast.

Change-Id: Id5d1863942848dd7a9e5e17e8180c33adbc72f15
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/34677
Reviewed-by: Anthony Gutierrez <anthony.gutierrez@amd.com>
Reviewed-by: Matt Sinclair <mattdsinclair@gmail.com>
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Anthony Gutierrez <anthony.gutierrez@amd.com>
Maintainer: Matt Sinclair <mattdsinclair@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>