KVM: arm64: selftests: Add a test case for a linked breakpoint

Currently, the debug-exceptions test doesn't have a test case for
a linked breakpoint. Add a test case for the linked breakpoint to
the test. The new test case uses a pair of breakpoints. One is the
higiest numbered context-aware breakpoint (for Context ID match),
and the other one is the breakpoint#0 (for Address Match), which
is linked to the context-aware breakpoint.

Signed-off-by: Reiji Watanabe <reijiw@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20221020054202.2119018-8-reijiw@google.com