ir3: Prevent oob writes to inputs/outputs array

ir3: Prevent oob writes to inputs/outputs array

Don't setup inputs and outputs if we aren't using
load_input/store_output intrinsics. While it's mostly harmless, there
may be more outputs than expected which would lead to an oob write of
the outputs array when setting the register id to INVALID_REG.

Also be more paranoid with asserts to catch this.

Fixes: a6291b1 ("freedreno/ir3: rework setup_{input,output} to make struct varyings work")
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7274>