hw/riscv: sifive_u: Make sure firmware info is 8-byte aligned

hw/riscv: sifive_u: Make sure firmware info is 8-byte aligned

Currently the firmware dynamic info (fw_dyn) is put right after
the reset vector, which is not 8-byte aligned on RV64. OpenSBI
fw_dynamic uses ld to read contents from 'struct fw_dynamic_info',
which expects fw_dyn to be on the 8-byte boundary, otherwise the
misaligned load exception may happen. Fortunately this does not
cause any issue on QEMU, as QEMU does support misaligned load.

RV32 does not have any issue as it is 4-byte aligned already.
Change to make sure it is 8-byte aligned which works for both
RV32 and RV64.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-id: 20210708143319.10441-1-bmeng.cn@gmail.com
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>