tpm: Revert tpm_tis_spi_mod.ko to tpm_tis_spi.ko.

Revert tpm_tis_spi_mod.ko back to tpm_tis_spi.ko as the rename could
break user space scripts. This can be achieved by renaming tpm_tis_spi.c
as tpm_tis_spi_main.c. Then tpm_tis_spi-y can be used inside the
makefile.

Cc: Andrey Pronin <apronin@chromium.org>
Cc: Stephen Boyd <swboyd@chromium.org>
Cc: stable@vger.kernel.org # 5.5.x
Fixes: 797c0113 ("tpm: tpm_tis_spi: Support cr50 devices")
Reported-by: Alexander Steffen <Alexander.Steffen@infineon.com>
Tested-by: Alexander Steffen <Alexander.Steffen@infineon.com>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>