[X86][SSE] Vector integer/float conversion memory folding (cvttps2dq / cvttpd2dq)

Fixed an issue with the (v)cvttps2dq and (v)cvttpd2dq instructions being incorrectly put in the 2 source operand folding tables instead of the 1 source operand and added the missing SSE/AVX versions.

Also added missing (v)cvtps2dq and (v)cvtpd2dq instructions to the folding tables.

Differential Revision: http://reviews.llvm.org/D6001