target/riscv: add 'parent' in profile description

target/riscv: add 'parent' in profile description

Certain S-mode profiles, like RVA22S64 and RVA23S64, mandate all the
mandatory extensions of their respective U-mode profiles. RVA22S64
includes all mandatory extensions of RVA22U64, and the same happens with
RVA23 profiles.

Add a 'parent' field to allow profiles to enable other profiles. This
will allow us to describe S-mode profiles by specifying their parent
U-mode profile, then adding just the S-mode specific extensions.

We're naming the field 'parent' to consider the possibility of other
uses (e.g. a s-mode profile including a previous s-mode profile) in the
future.

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: <20231218125334.37184-25-dbarboza@ventanamicro.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>