target/riscv: sync env->misa_ext* with cpu->cfg in realize()

target/riscv: sync env->misa_ext* with cpu->cfg in realize()

When riscv_cpu_realize() starts we're guaranteed to have cpu->cfg.ext_N
properties updated. The same can't be said about env->misa_ext*, since
the user might enable/disable MISA extensions in the command line, and
env->misa_ext* won't caught these changes. The current solution is to
sync everything at the end of validate_set_extensions(), checking every
cpu->cfg.ext_N value to do a set_misa() in the end.

The last change we're making in the MISA cfg flags are in the G
extension logic, enabling IMAFG if cpu->cfg_ext.g is enabled. Otherwise
we're not making any changes in MISA bits ever since realize() starts.

There's no reason to postpone misa_ext updates until the end of the
validation. Let's do it earlier, during realize(), in a new helper
called riscv_cpu_sync_misa_cfg(). If cpu->cfg.ext_g is enabled, do it
again by updating env->misa_ext* directly.

This is a pre-requisite to allow riscv_cpu_validate_set_extensions() to
use riscv_has_ext() instead of cpu->cfg.ext_N to validate the MISA
extensions, which is our end goal here.

Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Weiwei Li <liweiwei@iscas.ac.cn>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-Id: <20230406180351.570807-2-dbarboza@ventanamicro.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>