Let's drop the "shared" parameter from ram_block_add() and properly
store it in the flags of the ram block instead, such that
qemu_ram_is_shared() properly succeeds on all ram blocks that were mapped
MAP_SHARED.

We'll use this information next to fix some cases with shared anonymous
memory.

Reviewed-by: Igor Kotrasinski <i.kotrasinsk@partner.samsung.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20210406080126.24010-2-david@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>