Add preliminary RouterBoard RB1xx support

target/linux/rb1xx-2.6/Makefile

target/linux/rb1xx-2.6/config/default

target/linux/rb1xx-2.6/files/arch/mips/adm5120/Makefile

...et/linux/rb1xx-2.6/files/arch/mips/adm5120/adm5120_info.c

target/linux/rb1xx-2.6/files/arch/mips/adm5120/irq.c

target/linux/rb1xx-2.6/files/arch/mips/adm5120/memory.c

target/linux/rb1xx-2.6/files/arch/mips/adm5120/mipsIRQ.S

target/linux/rb1xx-2.6/files/arch/mips/adm5120/prom.c

target/linux/rb1xx-2.6/files/arch/mips/adm5120/setup.c

target/linux/rb1xx-2.6/files/arch/mips/pci/ops-adm5120.c

target/linux/rb1xx-2.6/files/arch/mips/pci/pci-adm5120.c

target/linux/rb1xx-2.6/files/drivers/char/adm5120_gpio.c

target/linux/rb1xx-2.6/files/drivers/mtd/nand/rbmipsnand.c

target/linux/rb1xx-2.6/files/drivers/net/adm5120sw.c

target/linux/rb1xx-2.6/files/drivers/net/adm5120sw.h

target/linux/rb1xx-2.6/files/drivers/serial/adm5120_uart.c

target/linux/rb1xx-2.6/files/drivers/usb/host/adm5120-hcd.c

...xx-2.6/files/include/asm-mips/mach-adm5120/adm5120_defs.h

...xx-2.6/files/include/asm-mips/mach-adm5120/adm5120_info.h

...-2.6/files/include/asm-mips/mach-adm5120/adm5120_switch.h