ARM: igep00x0.h: Enable the use of CMD_EXT4, CMD_FS_GENERIC and zImage.

Able to load the kernel from some form of ext[234] or FAT. Also, with v3.9 and
later of the Linux Kernel, uImage isn't builtable anymore by default, so we
should switch to use the bootz command.

Signed-off-by: Enric Balletbo i Serra <eballetbo@gmail.com>