gpu_compute: Support loading BLIT kernels

gpu_compute: Support loading BLIT kernels

The BLIT kernels used to implement DMA through the shaders don't fill
out all of the standard fields in an amd_kernel_code_t object.  This
patch modifies the code object parsing logic to support these new
kernels.

BLIT kernels are used in APUs when using ROCm memcopies for certain size
buffers, and are used for dGPUs when the SDMA engines are disabled.

Change-Id: Id4e667474d05e311097dbec443def07dfad14a79
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/29959
Maintainer: Anthony Gutierrez <anthony.gutierrez@amd.com>
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Matt Sinclair <mattdsinclair@gmail.com>