accel/tcg: Fix overwrite problems of tcg_cflags

accel/tcg: Fix overwrite problems of tcg_cflags

CPUs often set CF_PCREL in tcg_cflags before qemu_init_vcpu(), in which
tcg_cflags will be overwrited by tcg_cpu_init_cflags().

Fixes: 4be790263ffc ("accel/tcg: Replace `TARGET_TB_PCREL` with `CF_PCREL`")
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Weiwei Li <liweiwei@iscas.ac.cn>
Signed-off-by: Junqiang Wang <wangjunqiang@iscas.ac.cn>
Message-Id: <20230331150609.114401-6-liweiwei@iscas.ac.cn>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>