tpm: React correctly to RC_TESTING from TPM 2.0 self tests

The TPM can choose one of two ways to react to the TPM2_SelfTest command.
It can either run all self tests synchronously and then return RC_SUCCESS
once all tests were successful. Or it can choose to run the tests
asynchronously and return RC_TESTING immediately while the self tests still
execute in the background.

The previous implementation apparently was not aware of those possibilities
and attributed RC_TESTING to some prototype chips instead. With this change
the return code of TPM2_SelfTest is interpreted correctly, i.e. the self
test result is polled if and only if RC_TESTING is received.

Unfortunately, the polling cannot be done in the most straightforward way.
If RC_TESTING is received, ideally the code should now poll the
selfTestDone bit in the STS register, as this avoids sending more commands,
that might interrupt self tests executing in the background and thus
prevent them from ever completing. But it cannot be guaranteed that this
bit is correctly implemented for all devices, so the next best thing would
be to use TPM2_GetTestResult to query the test result. But the response to
that command can be very long, and the code currently lacks the
capabilities for efficient unmarshalling, so it is difficult to execute
this command.

Therefore, we simply run the TPM2_SelfTest command in a loop, which should
complete eventually, since we only request the execution of self tests that
have not yet been done.

Signed-off-by: Alexander Steffen <Alexander.Steffen@infineon.com>
Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Tested-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>

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