[SelectionDAG] Give all the target specific subclasses of SelectionDAGISel their own pass ID.

Previously we had a shared ID in SelectionDAGISel. AMDGPU has an
initializePass function for its subclass of SelectionDAGISel. No
other target does.

This causes all target specific SelectionDAGISel passes to be known
as "amdgpu-isel".

I'm not sure what would happen if another target tried to implement
an initializePass function too since the ID is already claimed.

This patch gives all targets their own ID and passes it down to
SelectionDAGISel constructor to MachineFunctionPass's constructor.

Unfortunately, I think this causes most targets to lose
print-before/after-all support for their SelectionDAGISel pass.
And they probably no longer support start/stop-before/after. We
can add initializePass functions to fix this as a follow up. NOTE:
This was probably also broken if the AMDGPU target isn't compiled in.

Step 1 to fixing PR59538.

Reviewed By: arsenm

Differential Revision: https://reviews.llvm.org/D140161