powerpc/corenet_ds: Slave module for boot from PCIE

powerpc/corenet_ds: Slave module for boot from PCIE

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

Slave's ucode and ENV can be stored in master's memory space, then slave
can fetch them through PCIE interface. For the corenet platform, ucode is
for Fman.

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

environment and requirement:

master:
	1. NOR flash for its own u-boot image, ucode and ENV space.
	2. Slave's u-boot image is in master NOR flash.
	3. Put the slave's ucode and ENV into it's own memory space.
	4. Normally boot from local NOR flash.
	5. Configure PCIE system if needed.
slave:
	1. Just has EEPROM for RCW. No flash for u-boot image, ucode and ENV.
	2. Boot location should be set to one PCIE interface by RCW.
	3. RCW should configure the SerDes, PCIE interfaces correctly.
	4. Must set all the cores in holdoff by RCW.
	5. Must be powered on before master's boot.

For the slave module, need to finish these processes:
	1. Set the boot location to one PCIE interface by RCW.
    2. Set a specific TLB entry for the boot process.
	3. Set a LAW entry with the TargetID of one PCIE for the boot.
	4. Set a specific TLB entry in order to fetch ucode and ENV from
	   master.
	5. Set a LAW entry with the TargetID one of the PCIE ports for
	   ucode and ENV.
	6. Slave's u-boot image should be generated specifically by
	   make xxxx_SRIO_PCIE_BOOT_config.
	   This will set SYS_TEXT_BASE=0xFFF80000 and other configurations.

In addition, the processes are very similar between boot from SRIO and
boot from PCIE. Some configurations like the address spaces can be set to
the same. So the module of boot from PCIE was added based on the existing
module of boot from SRIO, and the following changes were needed:
	1. Updated the README.srio-boot-corenet to add descriptions about
	   boot from PCIE, and change the name to
	   README.srio-pcie-boot-corenet.
	2. Changed the compile config "xxxx_SRIOBOOT_SLAVE" to
	   "xxxx_SRIO_PCIE_BOOT", and the image builded with
	   "xxxx_SRIO_PCIE_BOOT" can support both the boot from SRIO and
	   from PCIE.
	3. Updated other macros and documents if needed to add information
	   about boot from PCIE.

Signed-off-by: Liu Gang <Gang.Liu@freescale.com>
Signed-off-by: Andy Fleming <afleming@freescale.com>