gdb, amd-dbgapi-target: split wave_coordinates::to_string

gdb, amd-dbgapi-target: split wave_coordinates::to_string

wave_coordinates::to_string() produces a string in the following format:

  AMDGPU Wave a:q:d:w (x,y,z)/i

Split the method into smaller pieces:

  a:q:d:w   : hierarchy_str
  (x,y,z)   : workgroup_coord_str
  (x,y,z)/i : dispatch_pos_str

This is a refactoring to allow reusing pieces and also to let the code
document itself better.  Currently the reuse opportunity exists in the
downstream debugger.

Approved-By: Simon Marchi <simon.marchi@efficios.com>
Approved-by: Lancelot Six <lancelot.six@amd.com> (amdgpu)