KVM: x86/pmu: Update sample period in pmc_write_counter()

Update a PMC's sample period in pmc_write_counter() to deduplicate code
across all callers of pmc_write_counter().  Opportunistically move
pmc_write_counter() into pmc.c now that it's doing more work.  WRMSR isn't
such a hot path that an extra CALL+RET pair will be problematic, and the
order of function definitions needs to be changed anyways, i.e. now is a
convenient time to eat the churn.

Reviewed-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
Link: https://lore.kernel.org/r/20231103230541.352265-6-seanjc@google.com


Signed-off-by: Sean Christopherson <seanjc@google.com>