sparc: add {read,write}*_be routines

This patch adds {read,write}*_be big endian memory access
routines to the io.h header used on SPARC32 and SPARC64.

Tested on SPARC32 (LEON)

Signed-off-by: Jan Andersson <jan@gaisler.com>
Signed-off-by: David S. Miller <davem@davemloft.net>