KVM: arm64, x86: make kvm_arch_has_irq_bypass() inline

kvm_arch_has_irq_bypass() is a small function and even though it does
not appear in any *really* hot paths, it's also not entirely rare.
Make it inline---it also works out nicely in preparation for using it in
kvm-intel.ko and kvm-amd.ko, since the function is not currently exported.

Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>