Change all values in all limits.h for all architectures to signed decimal; the...

Change all values in all limits.h for all architectures to signed decimal; the hex values were not sign extending appropriate in most uses

git-svn-id: svn://svn.code.sf.net/p/nuttx/code/trunk@4911 42af7a65-404d-4744-a932-0658087f49c3