target/riscv: Remove condition guarding register zero for auipc and lui

target/riscv: Remove condition guarding register zero for auipc and lui

Commit 57c108b8646 introduced gen_set_gpri(), which already contains
a check for if the destination register is 'zero'. The check in auipc
and lui are then redundant. This patch removes those checks.

Signed-off-by: Víctor Colombo <victor.colombo@eldorado.org.br>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-Id: <20220610165517.47517-1-victor.colombo@eldorado.org.br>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>