AArch64: make sure jump table entries can reach entire image

This turns all jump table entries into deltas within the target
function because in the small memory model all code & static data must
be in a 4GB block somewhere in memory.

When the entries were a delta between the table location and a basic
block, the 32-bit signed entries are not enough to guarantee
reachability.

https://reviews.llvm.org/D87286