[CostModel][X86] Add SREM/UREM general and constant costs (PR38056)

We penalize general SDIV/UDIV costs but don't do the same for SREM/UREM.

This patch makes general vector SREM/UREM x20 as costly as scalar, the same approach as we do for SDIV/UDIV. The patch also extends the existing SDIV/UDIV constant costs for SREM/UREM - at the moment this means the additional cost of a MUL+SUB (see D48975).

Differential Revision: https://reviews.llvm.org/D48980

llvm-svn: 336486