Commit 4abd844d extended the fdt command parser to handle property
strings which are split across multiple arguments but it was broken for
byte streams and strings.

Byte stream parsing:

 * Fixes where it would terminate early or go into an endless loop.

 * Fixes a 0x00 being inserted into the data if there is a space after
   '[' or a separate argument.

 * Fixes dereferencing the argument pointer after the last argument.

 * Checks for bad characters.

String parsing:

 * Treat multiple arguments as a string list.  This fixes an issue where
   only the last argument was stored.

Signed-off-by: Ken MacLeod <ken@bitsko.slc.ut.us>