target/riscv: add Zvknha as an implied extension for Zvknhb

The RISC-V unpriv specification (zvk.adoc) states that "Zvknhb implies Zvknha". This means that enabling Zvknhb should automatically enable Zvknha. Add Zvknha to ZVKNHB_IMPLIED to ensure the dependency is correctly enforced. This issue was discovered and reported by SpecHunter, an AI-driven architecture specification analysis tool. Link:https://github.com/yizishun/rv-isa-sec/blob/master/output/riscv-isa-manual/pr-2635/qemu.txt Signed-off-by: Zishun Yi <vulab@iscas.ac.cn> Reviewed-by: Daniel Henrique Barboza <daniel.barboza@oss.qualcomm.com> Message-ID: <20260511051736.2916225-1-vulab@iscas.ac.cn> Signed-off-by: Alistair Francis <alistair.francis@wdc.com>