[X86][SSE] Added support for SSE3 lane duplication shuffle instructions

This patch adds shuffle matching for the SSE3 MOVDDUP, MOVSLDUP and MOVSHDUP instructions. The big use of these being that they avoid many single source shuffles from needing to use (pre-AVX) dual source instructions such as SHUFPD/SHUFPS: causing extra moves and preventing load folds.

Adding these instructions uncovered an issue in XFormVExtractWithShuffleIntoLoad which crashed on single operand shuffle instructions (now fixed). It also involved fixing getTargetShuffleMask to correctly identify theses instructions as unary shuffles.

Also adds a missing tablegen pattern for MOVDDUP.

Differential Revision: http://reviews.llvm.org/D7042

llvm-svn: 226716