ir3: Split regs into srcs and dsts array

While working on support for swz, it became clear that the quick solution I went with of IR3_REG_DEST for supporting multiple destinations was going to get a lot uglier once we started supporting instructions with multiple destinations in the post-RA scheduler. And I think that for handling shared registers, we'll need to handle this anyway as we cannot just emit a bunch of xor's on the spot (they need to be wrapped in a getone block to work properly) so we'll also need to emit an instruction with multiple destinations as part of parallelcopy lowering. So unfortunately I can't put off the big refactor we talked about, so here it is. There are actually three refactors:

• Splitting out array-write sources into their own register (needed for separate src/dst arrays and sane ir3_delayslots indexing)
• Making ir3_instruction::address a normal register rather than special casing it in foreach_ssa_src and a bunch of other places (also needed for sane ir3_delayslots indexing)
• Splitting ir3_instruction::regs into ir3_instruction::srcs and ir3_instruction::dsts

The last refactor is a little tricky, because it touches so many things, so it's split up: first we convert instruction producers to give separate src/dst sizes and use different functions to create sources and destinations, then we introduce ir3_instruction::srcs and ir3_instruction::dsts which for compatibility purposes alias ir3_instruction::regs, then we convert code manipulating regs to srcs and dsts piece by piece, after which we can finally remove the scaffolding and delete ir3_instruction::regs.

The end-result, beyond deleting a bunch of fiddly + 1's and even fiddlier code for parallel copies, is that the index passed into ir3_delayslots corresponds 1-to-1 with consumer->srcs, with no more adding/subtracting 1 in various places to paper over various differences in the indices. foreach_src_n will also no longer return something surprising in instructions with multiple destinations. I stopped short of splitting up ir3_register into ir3_source and ir3_dest though, since that would be a lot more refactoring and I don't need that yet.

Closes: #4731 (closed), #4732 (closed), #4733 (closed)