plat: marvell: a3700: do not power off cpu due to errata ref #13

Do not power off the CPU1 since there is no way to wake it up
(wake-up is causing CPU0 reset as well duo to HW bug). Quote from errata
Ref #13 [In power saving mode, both cores must be powered off]:
"When Core 0 is on and Core 1 is in power-off state, a Core 1
wake-up resets Core 0 as well and puts Core 0 back to ROM".

To overcome described HW bug instead of powering the CPU off, let it
reach WFI instruction, which is invoked by generic psci_do_cpu_off
function after platform handler finishes. This will put the core in low
power state and give a chance to wake it up.

Before this change, after running secondary kernel via kexec, only one
core was up, now both cores are up.

Change-Id: I87f144867550728055d9b8a2edb84a14539acab7
Signed-off-by: Grzegorz Jaszczyk <jaz@semihalf.com>
Reviewed-by: Kostya Porotchkin <kostap@marvell.com>

plat/marvell/a3700/common/plat_pm.c

@@ -288,18 +288,9 @@ int a3700_validate_ns_entrypoint(uintptr_t entrypoint)
  */
 void a3700_pwr_domain_off(const psci_power_state_t *target_state)
 {
-	uint32_t cpu_idx = plat_my_core_pos();
-
 	/* Prevent interrupts from spuriously waking up this cpu */
 	plat_marvell_gic_cpuif_disable();
 
-	/*
-	 * Enable Core VDD OFF, core is supposed to be powered
-	 * off by PMU when WFI command is issued.
-	 */
-	mmio_setbits_32(MVEBU_PM_CPU_0_PWR_CTRL_REG + 4 * cpu_idx,
-			MVEBU_PM_CORE_PD);
-
 	/* Core can not be powered down with pending IRQ,
 	 * acknowledge all the pending IRQ
 	 */