KVM: selftests: arm64: Fix steal_time test after UAPI refactoring

KVM: selftests: arm64: Fix steal_time test after UAPI refactoring

Fix the following failure to the steal_time test on arm64 by making
the timer address known to the guest.

==== Test Assertion Failure ====
  steal_time.c:229: !ret
  pid=18514 tid=18514 errno=22 - Invalid argument
     1  0x000000000040252f: check_steal_time_uapi at steal_time.c:229 (discriminator 20)
     2   (inlined by) main at steal_time.c:537 (discriminator 20)
     3  0x0000ffffa23d621b: ?? ??:0
     4  0x0000ffffa23d62fb: ?? ??:0
     5  0x0000000000402b6f: _start at ??:?
  KVM_SET_DEVICE_ATTR failed, rc: -1 errno: 22 (Invalid argument)

Fixes: 40351ed924dd ("KVM: selftests: Refactor UAPI tests into dedicated function")
Signed-off-by: Sebastian Ott <sebott@redhat.com>
Link: https://patch.msgid.link/20260504112808.21276-1-sebott@redhat.com
Signed-off-by: Marc Zyngier <maz@kernel.org>