refactor(sdei): use common create_spsr() in SDEI library

The current SPSR updation code as part of the SDEI interrupt handler
code is outdated. This patch replaces the legacy code with a call to
an up-to-date create_spsr()

Change-Id: I1f5fdd41dd14f4b09601310fe881fa3783d7f505
Signed-off-by: Arvind Ram Prakash <arvind.ramprakash@arm.com>
diff --git a/bl31/bl31_traps.c b/bl31/bl31_traps.c
index d14a91e..f1b1fa6 100644
--- a/bl31/bl31_traps.c
+++ b/bl31/bl31_traps.c
@@ -97,7 +97,7 @@
  * NOTE: This piece of code must be reviewed every release to ensure that
  * we keep up with new ARCH features which introduces a new SPSR bit.
  */
-static u_register_t create_spsr(u_register_t old_spsr, unsigned int target_el)
+u_register_t create_spsr(u_register_t old_spsr, unsigned int target_el)
 {
 	u_register_t new_spsr = 0;
 	u_register_t sctlr;