fs2dt: Fix for parsing/reading entries > 4k

[benmcollins]

The device-tree only does 4k reads at a time, so for entries greater than that, the fs2dt code would fail, assuming a single read would get the whole item.

Added helper function to continue reading as long as there was data and no errors.

This was evident from:

/proc/device-tree/soc@ffe000000/fman@400000/fman-firmware/fsl,firmware

On my P4080 system, which is 29668 bytes.

Signed-off-by: Ben Collins [email protected]

[barak]

Instead of defining its own auxiliary routine, I think this could now use slurp_file_len().