s390x/tcg: check for addressing exceptions for RRBE, SSKE and ISKE

s390x/tcg: check for addressing exceptions for RRBE, SSKE and ISKE

Let's replace the ram_size check by a proper physical address space
check (for example, to prepare for memory hotplug), trigger addressing
exceptions and trace the return value of the storage key getter/setter.

Provide an helper mmu_absolute_addr_valid() to be used in other context
soon. Always test for "read" instead of "write" as we are not actually
modifying the page itself.

Signed-off-by: David Hildenbrand <david@redhat.com>
Acked-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20210903155514.44772-5-david@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>