drm/xe: Only set xe_vma_op.map fields for GPUVA map operations

DRM_XE_VM_BIND_OP_MAP_* IOCTL operations can result in GPUVA unmap, remap,
or map operations in vm_bind_ioctl_ops_create. The xe_vma_op.map fields
are blindly set which is incorrect for GPUVA unmap or remap operations.
Fix this by only setting xe_vma_op.map for GPUVA map operations. Also
restructure a bit vm_bind_ioctl_ops_create to make the code a bit more
readable.

Reported-by: Dafna Hirschfeld <dhirschfeld@habana.ai>
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Brian Welty <brian.welty@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>