powerpc:Rename CONFIG_PBLRCW_CONFIG & CONFIG_SYS_FSL_PBL_PBI

Rename CONFIG_PBLRCW_CONFIG and CONFIG_PBLRCW_CONFIG.

Also add their details in README.

Signed-off-by: Prabhakar Kushwaha <prabhakar@freescale.com>
Reviewed-by: York Sun <yorksun@freescale.com>
diff --git a/README b/README
index aea82be..176de61 100644
--- a/README
+++ b/README
@@ -472,6 +472,15 @@
 		Board config to use DDR3. It can be enabled for SoCs with
 		Freescale DDR3 controllers.
 
+		CONFIG_SYS_FSL_PBL_PBI
+		It enables addition of RCW (Power on reset configuration) in built image.
+		Please refer doc/README.pblimage for more details
+
+		CONFIG_SYS_FSL_PBL_RCW
+		It adds PBI(pre-boot instructions) commands in u-boot build image.
+		PBI commands can be used to configure SoC before it starts the execution.
+		Please refer doc/README.pblimage for more details
+
 - Intel Monahans options:
 		CONFIG_SYS_MONAHANS_RUN_MODE_OSC_RATIO