tpm: moved tpm_register/remove_hardware() to tpm-chip.c

Moved tpm_register_hardware() and tpm_remove_harware() to
tpm-chip.c. Documentation of tpm_register_hardware() was
appended to the documentation of tpm_chip_register().

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