instruction: 0.463
syscall: 0.304
runtime: 0.232



RISC-V Regression: QEMU_CPU=f=false,zfinx=true gives misleading error message
Description of problem:
The f extension looks like it should be toggle-able using qemu_cpu since it doesn't throw error messages when specified.
Disabling the extension using f=false does not actually disable it as shown by the zfinx error message.
Eg. Unsupported extension is explicitly rejected
```
> QEMU_CPU=rv64,j=false ./qemu-riscv64 test.out
qemu-riscv64: can't apply global rv64-riscv-cpu.j=false: Property 'rv64-riscv-cpu.j' not found
```
Steps to reproduce:
1. Compile any riscv binary like: `int main() {}`
2. Execute using `QEMU_CPU=rv64,zfinx=true,f=false ./qemu-riscv64 test.out`