riscv disassembler error with pmpcfg0

[Eric DeVolder]

I've been using QEMU8 to collect instruction information on U-Boot + OpenSBI.

I'm running QEMU in this fashion to collect the information:

# qemu-system-riscv64 -plugin file=qemu/build/contrib/plugins/libexeclog.so 
-singlestep -d plugin,nochain -D execlog.txt ...

When examining the instruction trace in execlog, I've noticed that the 
disassembly for pmpcfg0 is erroneous, for example:

0, 0x5456, 0x3a002573, "csrrs                   a0,pmpcfg3,zero"

the CSR encoded in the instruction above is 0x3a0, which is pmpcfg0 (which also 
matches the code I'm examining).

For the Uboot+OpenSBI code I'm examining, pmpcfg0/3 is the only one that 
appears to have a problem.

I also checked QEMU9 and it behaves as described above as well.

I'm willing to provide a fix if I can get some advice/pointers on how this 
disassembly statement is generated...I did take a quick look but it didn't 
appear obvious how...

Thanks,
eric