[U-Boot] fdt performance

Hi all,

In our bootloader based off of 2013.07 we make extensive use of the flat device tree. In profiling our bootloader in our simulator I found that the function eating up the most time is fdt_next_tag. Looking at it, especially fdt_offset_ptr, it looks like there is a lot of room for improvement especially in the skip name section.

Some of the checks in fdt_offset_ptr also look useless, such as if ((offset + len) < offset) which will always be false, or if (p + len < p)

len is always positive.

-Aaron