ENGR00318392 ARM:imx6x: Save/restore SCU and some CP15 registers across suspend/resume

This patch ensures that the SCU and certain A9 CP15 registers state are maintained across
a suspend/resume cycle:
1. Need to ensure that SCU standby bit is set again after suspend/resume cycle, else
the system will never WAIT mode after a suspend/resume cycle. This bit should be enabled
on all SMP systems immaterial of whether CPUIDLE is enabled or not.
2. Several A9 errata workarounds involve setting bits in the ARM diagnostic register.
Save/restore this register across a suspend/resume cycle.
3. Save and restore the A9 power control register also.

Signed-off-by: Ranjani Vaidyanathan <Ranjani.Vaidyanathan@freescale.com>
(cherry picked from commit 7b5b4ef5b3cdc65c0576f87cfa52bcca1bda8b33)