ice: added sibling head to parse nodes

There was a bug in the previous code which never traverses all the
children to get the first node of the requested layer. Add a sibling
head pointer to point the first node of each layer per TC. This helps
traverse easier and quicker and also removes the recursion.

Signed-off-by: Victor Raj <victor.raj@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>