target/riscv/kvm: rename riscv_reg_id() to riscv_reg_id_ulong()

target/riscv/kvm: rename riscv_reg_id() to riscv_reg_id_ulong()

kvm_riscv_reg_id() returns an id encoded with an ulong size, i.e. an u32
size when running TARGET_RISCV32 and u64 when running TARGET_RISCV64.

Rename it to kvm_riscv_reg_id_ulong() to enhance code readability. It'll
be in line with the existing kvm_riscv_reg_id_<size>() helpers.

Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Message-ID: <20231208183835.2411523-6-dbarboza@ventanamicro.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>