SPM: Abstract NS configurations

Move configure_ns_code() operations into "Trustzone NS Agent" for the
IPC model. For the library model, move it into the library "main.c"
as a static function.

This abstraction leaves Trustzone specific operations to the Trustzone
NS Agent. The NS Agent thread entry keeps in assembly to accurately
control the stack usage.

Signed-off-by: Summer Qin <summer.qin@arm.com>
Change-Id: I25c3075627a418a1bc2f2f376d3eca6ddbc7aae0
9 files changed