tpm: Make tpm-dev allocate a per-file structure

This consolidates everything that is only used within tpm-dev.c
into tpm-dev.c and out of the publicly visible struct tpm_chip.

The per-file allocation lays the ground work for someday fixing the
strange forced O_EXCL behaviour of the current code.

Signed-off-by: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>
Reviewed-by: Joel Schopp <jschopp@linux.vnet.ibm.com>
Reviewed-by: Ashley Lai <adlai@linux.vnet.ibm.com>
Signed-off-by: Peter Huewe <peterhuewe@gmx.de>