add u-boot sources for danube

target/linux/ifxmips/image/Makefile

target/linux/ifxmips/image/u-boot/Makefile

...et/linux/ifxmips/image/u-boot/files/board/danube/Makefile

target/linux/ifxmips/image/u-boot/files/board/danube/README

...t/linux/ifxmips/image/u-boot/files/board/danube/config.mk

...et/linux/ifxmips/image/u-boot/files/board/danube/danube.c

...ux/ifxmips/image/u-boot/files/board/danube/ddr_settings.h

...fxmips/image/u-boot/files/board/danube/ddr_settings_111.h

...fxmips/image/u-boot/files/board/danube/ddr_settings_166.h

...age/u-boot/files/board/danube/ddr_settings_PROMOSDDR400.h

...mage/u-boot/files/board/danube/ddr_settings_Samsung_166.h

...xmips/image/u-boot/files/board/danube/ddr_settings_e111.h

...xmips/image/u-boot/files/board/danube/ddr_settings_e166.h

...ps/image/u-boot/files/board/danube/ddr_settings_psc_166.h

...xmips/image/u-boot/files/board/danube/ddr_settings_r111.h

...xmips/image/u-boot/files/board/danube/ddr_settings_r166.h

target/linux/ifxmips/image/u-boot/files/board/danube/flash.c

...x/ifxmips/image/u-boot/files/board/danube/lowlevel_init.S

...linux/ifxmips/image/u-boot/files/board/danube/pmuenable.S

...mips/image/u-boot/files/board/danube/u-boot-bootstrap.lds