tpm: Prevent hwrng from activating during resume

Set TPM_CHIP_FLAG_SUSPENDED in tpm_pm_suspend() and reset in
tpm_pm_resume(). While the flag is set, tpm_hwrng() gives back zero
bytes. This prevents hwrng from racing during resume.

Cc: stable@vger.kernel.org
Fixes: 6e592a06 ("tpm: Move Linux RNG connection to hwrng")
Reviewed-by: Jerry Snitselaar <jsnitsel@redhat.com>
Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>