tpm: style and ordering fixes for v3 patch set

- Remove dev_err() messages after tpmm_chip_alloc() and tpm_chip_register().
- Use devm_request_irq() and devm_free_irq() in tpm_tis.c.
- Fix the order of tpm_chip_register() call in xen-tpmfront.c.
- Fix the order of tpm_chip_unregister() call in tpm_nsc.c.
- Add comment about possible issue when releasing a platform driver in
  tpm_tis.c.

Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>