Refactor the endianness conversion functions and header files.

The endianness of an architecture is now set up automatically using Kconfig
and some common code. The available conversion functions were also expanded
to go to or from a particular endianness. Those use the abbreviation le or be
for little or big endian.

Built for Stumpy and saw coreinfo cbfs support work which uses network
byte order. Used the functions which convert to little endian to implement an
AHCI driver. The source arch is also little endian, so they were effectively
(and successfully) inert.

Change-Id: I3a2d2403855b3e0e93fa34f45e8e542b3e5afeac
Signed-off-by: Gabe Black <gabeblack@google.com>
Reviewed-on: http://review.coreboot.org/1719
Tested-by: build bot (Jenkins)
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>

payloads/libpayload/libc/lar.c

@@ -27,8 +27,8 @@
  * SUCH DAMAGE.
  */
 
+#include <endian.h>
 #include <libpayload.h>
-#include <arch/endian.h>
 
 #define ROM_RESET_VECTOR 0xFFFFFFF0