tpm: only attempt to disable the LPC CLKRUN if is already enabled

Commit 5e572cab ("tpm: Enable CLKRUN protocol for Braswell systems")
added logic in the TPM TIS driver to disable the Low Pin Count CLKRUN
signal during TPM transactions.

Unfortunately this breaks other devices that are attached to the LPC bus
like for example PS/2 mouse and keyboards.

One flaw with the logic is that it assumes that the CLKRUN is always
enabled, and so it unconditionally enables it after a TPM transaction.

But it could be that the CLKRUN# signal was already disabled in the LPC
bus and so after the driver probes, CLKRUN_EN will remain enabled which
may break other devices that are attached to the LPC bus but don't have
support for the CLKRUN protocol.

Fixes: 5e572cab ("tpm: Enable CLKRUN protocol for Braswell systems")
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Tested-by: James Ettle <james@ettle.org.uk>
Tested-by: Jeffery Miller <jmiller@neverware.com>
Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Tested-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>