Incorrect performance counter

[jserv]

@ypaskell implemented a number of 64-bit read-only user-level counters, including CSR_CYCLE and CSR_CYCLEH (#33).

The procedure to validate:

make clean
rm -rf src/mini-gdbstub
git reset --hard 53a6f9463c4b344746cb1154cbfb995e44f30300
make
build/rv32emu build/perfcount.elf

Output:

cycle count: 1728
instret: 174
Sparkle state:
4DF96879 8C7C2C33
82236B4A 904F4DD7
D6A030E8 F03B09AA
C4C3BB34 F063DFF9
61F9CEFF 8EC21FFA
93DF370F 83ACF1E2

However, in recent commits, both CSR_CYCLE and CSR_CYCLEH fail to deliver the expected values.

$ build/rv32emu build/perfcount.elf 
cycle count: 0
instret: 0
Sparkle state:
4DF96879 8C7C2C33
82236B4A 904F4DD7
D6A030E8 F03B09AA
C4C3BB34 F063DFF9
61F9CEFF 8EC21FFA
93DF370F 83ACF1E2

There is no increment for both cycle count and instret.