SPM: Refine the get_irq_line_for_signal function

This patch moves the signal bit check from calller to
get_irq_line_for_signal().
The check should have been included in the function.

Change-Id: Ic2b850ecc02ed3ce6477781cfcf213b5aa202db7
Signed-off-by: Kevin Peng <kevin.peng@arm.com>
4 files changed