Let's separate the compilation of tpm_tis_common.c from
the compilation of tpm_tis_isa.c

The common part will be also compiled along with the
tpm_tis_sysbus device.

Signed-off-by: Eric Auger <eric.auger@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Tested-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Message-id: 20200305165149.618-5-eric.auger@redhat.com
Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>