tpm: have event log use the tpm_chip

Move the backing memory for the event log into tpm_chip and push
the tpm_chip into read_log. This optimizes read_log processing by
only doing it once and prepares things for the next patches in the
series which require the tpm_chip to locate the event log via
ACPI and OF handles instead of searching.

This is straightfoward except for the issue of passing a kref through
i_private with securityfs. Since securityfs_remove does not have any
removal fencing like sysfs we use the inode lock to safely get a
kref on the tpm_chip.

Suggested-by: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>
Signed-off-by: Nayna Jain <nayna@linux.vnet.ibm.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>