SPM: Only loads partition irqs when exist

In case of no irqs in all partitions, there is no need
to keep the partition irqs load logic code and irqs context
in partition load info.
This patch decrease 200 bytes code size.

Signed-off-by: Sherry Zhang <sherry.zhang2@arm.com>
Change-Id: I93f72fb180aac7035f51ed8af4700220d54feb85
12 files changed