[mlir][ArmSVE] Restructure sources to match ArmSME dialect (NFC) (#68399)

This rearranges the Arm SVE dialect to have the same structure of the
Arm SME dialect. So this just moves around some source files and adds a
ArmSVE_IntrOp base class for SVE intrinsics. This makes later changes a
little easier and more consistent other dialects.