[OpenMP] Change `__tgt_device_image` to point to the image (#77003)

Summary:
We use the OffloadBinary to contain bundled offloading objects used to
support many images / targets at the same time. The `__tgt_device_info`
struct used to contain a pointer to this underlying binary format, which
contains information about the triple and architecture. We used to parse
this in the runtime to do image verification.

Recent changes removed the need for this to be used internally, as we
just parse it out of the ELF directly. This patch sets the pointers up
so they point to the ELF without requiring any further parsing.