Now that we can have multiple .c files in the tpm module there is
no reason for tpm-bios.

tpm-bios exported several functions: tpm_bios_log_setup,
tpm_bios_log_teardown, tpm_add_ppi, and tpm_remove_ppi.

They are only used by tpm, and if tpm-bios is built then
tpm will unconditionally require them. Further, tpm-bios does
nothing on its own, it has no module_init function.

Thus we remove the exports and merge the modules to simplify things.

The Makefile conditions are changed slightly to match the code,
tpm_ppi is always required if CONFIG_ACPI is set.
Signed-off-by: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>