powerpc/corenet_ds: Slave reads ENV from master when boot from SRIO

When boot from SRIO, slave's ENV can be stored in master's memory space,
then slave can fetch the ENV through SRIO interface.

NOTE: Because the slave can not erase, write master's NOR flash by SRIO
	  interface, so it can not modify the ENV parameters stored in
	  master's NOR flash using "saveenv" or other commands.

Master needs to:
	1. Put the slave's ENV into it's own memory space.
	2. Set an inbound SRIO window covered slave's ENV stored in master's
	   memory space.
Slave needs to:
	1. Set a specific TLB entry in order to fetch ucode and ENV from master.
	2. Set a LAW entry with the TargetID SRIO1 or SRIO2 for ucode and ENV.

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

README

@@ -3026,6 +3026,24 @@ to save the current settings.
 	  environment area within the total memory of your DataFlash placed
 	  at the specified address.
 
+- CONFIG_ENV_IS_IN_REMOTE:
+
+	Define this if you have a remote memory space which you
+	want to use for the local device's environment.
+
+	- CONFIG_ENV_ADDR:
+	- CONFIG_ENV_SIZE:
+
+	  These two #defines specify the address and size of the
+	  environment area within the remote memory space. The
+	  local device can get the environment from remote memory
+	  space by SRIO or other links.
+
+BE CAREFUL! For some special cases, the local device can not use
+"saveenv" command. For example, the local device will get the
+environment stored in a remote NOR flash by SRIO link, but it can
+not erase, write this NOR flash by SRIO interface.
+
 - CONFIG_ENV_IS_IN_NAND:
 
 	Define this if you have a NAND device which you want to use