LoongArch: KVM: Get VM PMU capability from HW GCFG register

LoongArch: KVM: Get VM PMU capability from HW GCFG register

Now VM PMU capability comes from host PMU capability directly, instead
bit 23 of HW GCFG CSR register also show PMU capability for VM. It will
be better if it comes from HW GCFG CSR register rather than just host
PMU capability, especially when LVZ feature is emulated in TCG mode, in
which case without PMU capability.

Signed-off-by: Bibo Mao <maobibo@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>