[mlir][ArmSME] Remove "pure" side-effect from 'get_tile_id' op to prevent CSE

The 'get_tile_id' op is currently marked as pure so CSE thinks these ops
are equivalent and replaces with them a single one. This patch removes
pure to prevent this.

Reviewed By: awarzynski

Differential Revision: https://reviews.llvm.org/D156558