tpm2: tis_spi: add linux compatible fallback string

tpm2: tis_spi: add linux compatible fallback string

This solves a compatibility issue with Linux device trees
that contain TPMv2.x hardware. So it's easier to import DTS
from upstream kernel when migrating board init from C code
to DTS.

The issue is that fallback binding is different between Linux
and u-Boot.

Linux: "tcg,tpm_tis-spi"
U-Boot: "tis,tpm2-spi"

As there are currently no in-tree users of the U-Boot binding,
it makes sense to use Linux fallback binding.

Signed-off-by: Bruno Thomsen <bruno.thomsen@gmail.com>
Reviewed-by: Tom Rini <trini@konsulko.com>