pytest: add test script to validate Firmware Handoff

pytest: add test script to validate Firmware Handoff

Add test cases to validate FDT and TPM eventlog handoff from TF-A
and OP-TEE via bloblist.

For FDT, the nodes 'reserved-memory' and 'firmware' appended by
OP-TEE indicates a successful handoff.

For TPM eventlog, the events 'SECURE_RT_EL3', 'SECURE_RT_EL1_OPTEE'
and 'SECURE_RT_EL1_OPTEE_EXTRA1' created by TF-A indicates a
successful handoff.

Signed-off-by: Raymond Mao <raymond.mao@linaro.org>
Reviewed-by: Tom Rini <trini@konsulko.com>