KVM: x86/pmu: Move kvm_init_pmu_capability() to pmu.c

KVM: x86/pmu: Move kvm_init_pmu_capability() to pmu.c

Move kvm_init_pmu_capability() to pmu.c so that future changes can access
variables that have no business being visible outside of pmu.c.
kvm_init_pmu_capability() is called once per module load, there's is zero
reason it needs to be inlined.

No functional change intended.

Cc: Dapeng Mi <dapeng1.mi@linux.intel.com>
Cc: Sandipan Das <sandipan.das@amd.com>
Reviewed-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
Link: https://lore.kernel.org/r/20250805190526.1453366-10-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>