fix(cm): update gic el2 sysregs save/restore mechanism

This patch does following two changes
- Create a separate routine for saving/restoring GIC el2 system registers
- To access ICC_SRE_EL2 register there was a workaround to set
  SCR_EL3.NS before accessing it. This was required because SCR_EL3.EEL2
  was zero. But with commit f105dd5fa this bit has been set to one early
  on in booting process for a system with FEAT_SEL2 present and S-EL2
  enabled.
  However, we still need the workaround for a system which needs
  save/restore of EL2 registers without secure EL2 being enabled e.g.
  system with Non-secure and Realm world present.

Signed-off-by: Manish Pandey <manish.pandey2@arm.com>
Change-Id: I8d55c3dc6a17c4749748822d4a738912c1e13298
1 file changed