[PATCH] fix T-HEAD c9xx cpu softlock

[刘海蛟]

These patches fix the system hang issue caused by using perf tool on
T-HEAD c9xx related platforms.

When detecting features of PMU, MHPMCOUNTER3 is changed to 0xffffffffffffffff
in the function hart_mhpm_get_allowed_bits. Enabling the counter directly would
cause an overflow interrupt. The correct procedure is to initialize
the counter's initial
value before enabling the counter to count.
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