LoongArch: KVM: Move some variable declarations to paravirt.h

LoongArch: KVM: Move some variable declarations to paravirt.h

Some variables relative with paravirt feature are declared in the header
file asm/qspinlock.h, however this file can be included only when option
CONFIG_SMP is on. There is compiling warnings if CONFIG_SMP is off since
variables are not declared.

Move these variable declarations to header file asm/paravirt.h to avoid
compiling warnings.

Fixes: c43dce6f13fb ("LoongArch: KVM: Make vcpu_is_preempted() as a macro rather than function")
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202605061313.O8Hswm2b-lkp@intel.com/
Signed-off-by: Bibo Mao <maobibo@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>