target/arm/kvm: Make uncalled stubs explicitly unreachable

target/arm/kvm: Make uncalled stubs explicitly unreachable

When we compile without KVM support !defined(CONFIG_KVM) we generate
stubs for functions that the linker will still encounter. Sometimes
these stubs can be executed safely and are placed in paths where they
get executed with or without KVM. Other functions should never be
called without KVM. Those functions should be guarded by kvm_enabled(),
but should also be robust to refactoring mistakes. Putting a
g_assert_not_reached() in the function should help. Additionally,
the g_assert_not_reached() calls may actually help the linker remove
some code.

We remove the stubs for kvm_arm_get/put_virtual_time(), as they aren't
necessary at all - the only caller is in kvm.c

Reviewed-by: Eric Auger <eric.auger@redhat.com>
Signed-off-by: Andrew Jones <drjones@redhat.com>
Message-id: 20201001061718.101915-3-drjones@redhat.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>