selftests: KVM: Test OS lock behavior

KVM now correctly handles the OS Lock for its guests. When set, KVM
blocks all debug exceptions originating from the guest. Add test cases
to the debug-exceptions test to assert that software breakpoint,
hardware breakpoint, watchpoint, and single-step exceptions are in fact
blocked.

Signed-off-by: Oliver Upton <oupton@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20220203174159.2887882-7-oupton@google.com