SiP: MISRA fixes for execution state switch

These changes address most of the required MISRA rules. In the process,
some from generic code is also fixed.

No functional changes.

Change-Id: I707dbec9b34b802397e99da2f5ae738165d6feba
Signed-off-by: Jeenu Viswambharan <jeenu.viswambharan@arm.com>