[GlobalISel][AArch64] Add support for @llvm.ceil

This adds a G_FCEIL generic instruction and uses it in AArch64. This adds
selection for floating point ceil where it has a supported, dedicated
instruction. Other cases aren't handled here.

It updates the relevant gisel tests and adds a select-ceil test. It also adds a
check to arm64-vcvt.ll which ensures that we don't fall back when we run into
one of the relevant cases.

llvm-svn: 349664