KVM: selftests: Convert set_memory_region_test to printf-based GUEST_ASSERT

Convert set_memory_region_test to print-based GUEST_ASSERT, using a combo
of newfangled macros to report (hopefully) useful information.

Link: https://lore.kernel.org/r/20230729003643.1053367-19-seanjc@google.com


Signed-off-by: Sean Christopherson <seanjc@google.com>