Fixed SEA IR bugs.

Bug 1: The type inference visitor did not clear type between visits,
so all instructions had types attached because of this.

Bug 2: The .dot file genration was missing phi ssa edges because
the GetSSAProducers map hasn't got the same semantics.
(Phi Nodes use a single register which has multiple definitions,
not multiple registers with a single definition each)

Bug 3: Added the SE IR id in the textual representation of nodes
in the .dot representation to ease debugging.

Change-Id: Iccbce6f7a3ffba044677c2d548d26af62223be15