Replace buffer load/store intrinsics with builtins

[illsilin]

Proposed changes

The names of the buffer load/store intrinsics are going to change in the future compiler versions. One way to avoid compilation errors is to switch from intrinsics to built-ins. Unfortunately, it doesn't look like built-ins available for every intrinsic we use. Also, these built-ins won't be available until the next ROCm release, so we won't be able to merge these changes right away.
However, I've tested these changes with the future compiler versions and made sure that the code builds and the unit tests are passing.