[lib][debug] tweak the hexdump and dw debug commands to be a bit more useful

-hexdump8 now stops dumping before it hits the end of the 16 byte line
-d[bhw] remembers the last size and offset you used
[arch][arm] fix a few bugs in the stackusage script
[include][endian] add 64bit byte swap macros
[include][err] add new error codes and properly surround with ()
[kernel] add a few convenience routines