[CostModel][AArch64] Increase cost of vector insert element and add missing cast costs

Summary:
Increase the estimated costs for insert/extract element operations on
AArch64. This is motivated by results from benchmarking interleaved
accesses.

Add missing costs for zext/sext/trunc instructions and some integer to
floating point conversions. These costs were previously calculated
by scalarizing these operation and were affected by the cost increase of
the insert/extract element operations.

Reviewers: rengolin

Subscribers: mcrosier, aemerson, rengolin, llvm-commits

Differential Revision: http://reviews.llvm.org/D11939

llvm-svn: 245226