RISC-V panics on booting after r353294

[Mark Johnston]

On Tue, Oct 08, 2019 at 04:52:19PM +0800, Li-Wen Hsu wrote:
> Hi Mark,
> 
> I found that FreeBSD-head-riscv64-test is failing after this build:
> 
> https://ci.freebsd.org/job/FreeBSD-head-riscv64-test/12203/
> 
> I suspect r353294 changed some VM stuff and caused this.
> 
> Can you help check this? Thanks!

Thanks Li-Wen.  I reproduced the panic; it should be fixed by r353306.