ppc4xx: Add Sequoia RAM-booting target

ppc4xx: Add Sequoia RAM-booting target

This patch adds another build target for the AMCC Sequoia PPC440EPx
eval board. This RAM-booting version is targeted for boards without
NOR FLASH (NAND booting) which need a possibility to initially
program their NAND FLASH. Using a JTAG debugger (e.g. BDI2000/3000)
configured to setup the SDRAM, this debugger can load this RAM-
booting image to the target address in SDRAM (in this case 0x1000000)
and start it there. Then U-Boot's standard NAND commands can be
used to program the NAND FLASH (e.g. "nand write ...").

Here the commands to load and start this image from the BDI2000:

440EPX>reset halt
440EPX>load 0x1000000 /tftpboot/sequoia/u-boot.bin
440EPX>go 0x1000000

Please note that this image automatically scans for an already
initialized SDRAM TLB (detected by EPN=0). This TLB will not be
cleared. This TLB doesn't need to be TLB #0, this RAM-booting
version will detect it and preserve it. So booting via BDI2000
will work and booting with a complete different TLB init via
U-Boot works as well.

Signed-off-by: Stefan Roese <sr@denx.de>