[Aarch64] Add cost for missing extensions.

This patch adds a cost estimate for some missing sign and zero extensions. The
costs were determined by counting the number of shift instructions generated
without context for each new extension.

Differential Revision: http://reviews.llvm.org/D14730

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@253482 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed