freedreno: Split ir3_const's user buffer and indirect upload APIs.

freedreno: Split ir3_const's user buffer and indirect upload APIs.

They're almost entirely split by whether you're uploading user buffer or
from a BO.  While I'm rewriting the API, drop the emit_const ->
fdN_emit_const wrapper in favor of a #define before the header and a
little helper for the asserts.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5990>