Moves the comments from the k_fifo.c to the fifo.h file. Only the
external API information was moved. Minor edits were performed to adapt
the comments to different parameters and aliases.
Change-Id: I69d2d009f7ec6390e0a2fc9d6a346ddc0111f9f1
Signed-off-by: Rodrigo Caballero <rodrigo.caballero.abraham@intel.com>
Signed-off-by: Anas Nashif <anas.nashif@intel.com>