hw/riscv/riscv-iommu: Fixup PDT Nested Walk

hw/riscv/riscv-iommu: Fixup PDT Nested Walk

Current implementation is wrong when iohgatp != bare. The RISC-V
IOMMU specification has defined that the PDT is based on GPA, not
SPA. So this patch fixes the problem, making PDT walk correctly
when the G-stage table walk is enabled.

Fixes: 0c54acb8243d ("hw/riscv: add RISC-V IOMMU base emulation")
Cc: qemu-stable@nongnu.org
Cc: Sebastien Boeuf <seb@rivosinc.com>
Cc: Tomasz Jeznach <tjeznach@rivosinc.com>
Reviewed-by: Weiwei Li <liwei1518@gmail.com>
Reviewed-by: Nutty Liu <liujingqi@lanxincomputing.com>
Signed-off-by: Guo Ren (Alibaba DAMO Academy) <guoren@kernel.org>
Tested-by: Chen Pei <cp0613@linux.alibaba.com>
Tested-by: Fangyu Yu <fangyu.yu@linux.alibaba.com>
Message-ID: <20250913041233.972870-1-guoren@kernel.org>
[ Changes by AF:
 - Add braces to if statements
]
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
(cherry picked from commit 15abfced803929f935bb59a0e1b02558bd8325c4)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>