linux-user: remove nmi.c and fw-path-provider.c

linux-user binaries don't need firmware and NMI,
so don't add them in this case, move QDEV
firmware functions to qdev-fw.c

Signed-off-by: Laurent Vivier <laurent@vivier.eu>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20171103193802.11876-1-laurent@vivier.eu>