hw/riscv: add riscv-iommu-bits.h

hw/riscv: add riscv-iommu-bits.h

This header will be used by the RISC-V IOMMU emulation to be added
in the next patch. Due to its size it's being sent in separate for
an easier review.

One thing to notice is that this header can be replaced by the future
Linux RISC-V IOMMU driver header, which would become a linux-header we
would import instead of keeping our own. The Linux implementation isn't
upstream yet so for now we'll have to manage riscv-iommu-bits.h.

Signed-off-by: Tomasz Jeznach <tjeznach@rivosinc.com>
Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Frank Chang <frank.chang@sifive.com>
Reviewed-by: Jason Chien <jason.chien@sifive.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-ID: <20241016204038.649340-3-dbarboza@ventanamicro.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>