target/riscv: add profile u_parent and s_parent

target/riscv: add profile u_parent and s_parent

The current 'parent' mechanic for profiles allows for one profile to be
a child of a previous/older profile, enabling all its extensions (and
the parent profile itself) and sparing us from tediously listing all
extensions for every profile.

This works fine for u-mode profiles. For s-mode profiles this is not
enough: a s-mode profile extends not only his equivalent u-mode profile
but also the previous s-mode profile. This means, for example, that
RVA23S64 extends both RVA23U64 and RVA22S64.

To fit this usage, rename the existing 'parent' to 'u_parent' and add a
new 's_parent' attribute for profiles. Handle both like we were doing
with the previous 'parent' attribute, i.e. if set, enable it. This
change does nothing for the existing profiles but will make RVA23S64
simpler.

Suggested-by: Andrew Jones <ajones@ventanamicro.com>
Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-ID: <20250115184316.2344583-4-dbarboza@ventanamicro.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>