tpm: replace dynamically allocated bios_dir with a static array

This commit is based on a commit by Nayna Jain. Replaced dynamically
allocated bios_dir with a static array as the size is always constant.

Suggested-by: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>