powerpc/corenet_ds: Slave core in holdoff when boot from SRIO

When boot from SRIO, slave's core can be in holdoff after powered on for
some specific requirements. Master can release the slave's core at the
right time by SRIO interface.

Master needs to:
	1. Set outbound SRIO windows in order to configure slave's registers
	   for the core's releasing.
	2. Check the SRIO port status when release slave core, if no errors,
	   will implement the process of the slave core's releasing.
Slave needs to:
	1. Set all the cores in holdoff by RCW.
	2. Be powered on before master's boot.

Signed-off-by: Liu Gang <Gang.Liu@freescale.com>
Signed-off-by: Shaohui Xie <Shaohui.Xie@freescale.com>