Split texkill_cond into texkill_unary (single source) and texkill_binary
(two sources) variants. Update the compiler to use ISA_OPC_TEXKILL_UNARY for
discard emission since it only uses a single source operand.
Fixes: 081efcd68d ("etnaviv: isa: Split texkill into concrete bitset variants")
Signed-off-by: Christian Gmeiner <cgmeiner@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/40262>