Core: Make error handling more strict

Change the core and SPM behaviour from returning error code to panic,
in the following cases:
 - tfm_core_partition_request called from Thread mode
 - secure lock is held in case of a non-secure secure service caller
 - Partition state check fails when starting IRQ handler
 - Secure SVC handler receives a NS EXC_RET value

Change-Id: Ied6ab7c2ffb2be25a7ffa3b4ef1dc20783fccc4c
Signed-off-by: Mate Toth-Pal <mate.toth-pal@arm.com>