target/riscv/kvm: change KVM_REG_RISCV_FP_F to u32

target/riscv/kvm: change KVM_REG_RISCV_FP_F to u32

KVM_REG_RISCV_FP_F regs have u32 size according to the API, but by using
kvm_riscv_reg_id() in RISCV_FP_F_REG() we're returning u64 sizes when
running with TARGET_RISCV64. The most likely reason why no one noticed
this is because we're not implementing kvm_cpu_synchronize_state() in
RISC-V yet.

Create a new helper that returns a KVM ID with u32 size and use it in
RISCV_FP_F_REG().

Reported-by: Andrew Jones <ajones@ventanamicro.com>
Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Message-ID: <20231208183835.2411523-2-dbarboza@ventanamicro.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>