tpm: cr50: Check for valid locality

tpm: cr50: Check for valid locality

When the Cr50 starts up it doesn't have a valid locality. The driver sets
it to -1 to indicate that. Tracking this allows cr50_i2c_cleanup() to
avoid releasing a locality that was not claimed.

However the helper functions that generate the flags use a u8 type which
cannot support -1, so they return a locality of 0xff.

Fix this by updating the type. With this, 'tpm startup TPM2_SU_CLEAR'
works as expected.

Signed-off-by: Simon Glass <sjg@chromium.org>