AARCH64 Illegal Instruction (CurrentEL)
Description of problem:
While emulating Aarch64 in QEMU, whenever the instruction `CurrentEL` is executed,
QEMU crashes with the following message.

`qemu: uncaught target signal 4 (Illegal instruction) - core dumped
Illegal instruction (core dumped)`

I've tried both QEMU user space translation (qemu-aarch64-static) and QEMU emulation (qemu-system-aarch64),
and both fail with the above message.

C Code to reproduce bug, courtesy of https://github.com/cirosantilli/linux-kernel-module-cheat/blob/35684b1b7e0a04a68987056cb15abd97e3d2f0cc/baremetal/arch/aarch64/el.c
```
#include <stdio.h>
#include <inttypes.h>

int main(void) {
        register uint64_t x0 __asm__ ("x0");
	__asm__ ("mrs x0, CurrentEL;" : : : "%x0");
	printf("%" PRIu64 "\n", x0 >> 2);
	return 0;
}
```
Steps to reproduce:
1. Copy C code above into file.
2. Compile code `gcc ./main.c --static`
3. Execute elf bin `./a.out`
Additional information: