QEMU bug: csrw `MIE_MEIE | MIE_MSIE | MIE_MTIE` to sie changes mie
Description of problem:
QEMU bug: csrw `MIE_MEIE | MIE_MSIE | MIE_MTIE` to sie changes mie.

**Only csrw causes this bug. csrs/csrc have no effect.**
Steps to reproduce:
output from my test program: 
```
[firmware_main] Clear mie
[firmware_main] mie is 0x0
[firmware_main] sie is 0x0
[firmware_main] Set MIE_SEIE | MIE_STIE | MIE_SSIE | MIE_MEIE for mie
[firmware_main] mie is 0xa22
[firmware_main] sie is 0x0
[firmware_main] mideleg is 0x0
[firmware_main] Set MIE_SEIE | MIE_STIE | MIE_SSIE for mideleg
[firmware_main] mie is 0xa22
[firmware_main] sie is 0x222
[firmware_main] Set MIE_SSIE for sie
[firmware_main] mie is 0x800
[firmware_main] sie is 0x0
```