powerpc/tool/pbl: fix pbl image compiling process

Previous process of compiling a PBL boot image is:
1: make <board_name_config>
2: make u-boot.pbl

for example:
make T4240QDS_SDCARD_config
make u-boot.pbl

Now the process is:
1: make <board_name>

for example:
make T4240QDS_SDCARD

Also, updated README.pblimage.
Signed-off-by: NShaohui Xie <Shaohui.Xie@freescale.com>

Makefile

@@ -398,6 +398,7 @@ ALL-y += $(obj)u-boot.srec $(obj)u-boot.bin $(obj)System.map
 
 ALL-$(CONFIG_NAND_U_BOOT) += $(obj)u-boot-nand.bin
 ALL-$(CONFIG_ONENAND_U_BOOT) += $(obj)u-boot-onenand.bin
+ALL-$(CONFIG_RAMBOOT_PBL) += $(obj)u-boot.pbl
 ALL-$(CONFIG_SPL) += $(obj)spl/u-boot-spl.bin
 ALL-$(CONFIG_SPL_FRAMEWORK) += $(obj)u-boot.img
 ALL-$(CONFIG_TPL) += $(obj)tpl/u-boot-tpl.bin

doc/README.pblimage

@@ -14,20 +14,17 @@ Building PBL Boot Image and boot steps
 1. Building PBL Boot Image.
    The default Image is u-boot.pbl.
 
-   For eSPI boot(available on P3041/P4080/P5020):
+   For eSPI boot(available on P2041/P3041/P4080/P5020/P5040/T4240):
 	To build the eSPI boot image:
-	make <board_name>_SPIFLASH_config
-	make u-boot.pbl
+	make <board_name>_SPIFLASH
 
-   For SD boot(available on P3041/P4080/P5020):
+   For SD boot(available on P2041/P3041/P4080/P5020/P5040/T4240):
 	To build the SD boot image:
-	make <board_name>_SDCARD_config
-	make u-boot.pbl
+	make <board_name>_SDCARD
 
-   For Nand boot(available on P3041/P5020):
+   For Nand boot(available on P2041/P3041/P5020/P5040):
 	To build the NAND boot image:
-	make <board_name>_NAND_config
-	make u-boot.pbl
+	make <board_name>_NAND
 
 
 2. pblimage support available with mkimage utility will generate Freescale PBL