arch/powerpc/lib/board.c, *traps.c: sparse fixes

traps.c:*:1: warning: symbol 'print_backtrace' was not declared. Should it be static?
traps.c:93:1: warning: symbol '_exception' was not declared. Should it be static?
board.c:166:6: warning: symbol '__board_add_ram_info' was not declared. Should it be static?
board.c:174:5: warning: symbol '__board_flash_wp_on' was not declared. Should it be static?
board.c:187:6: warning: symbol '__cpu_secondary_init_r' was not declared. Should it be static?
board.c:265:12: warning: symbol 'init_sequence' was not declared. Should it be static?
board.c:348:5: warning: symbol '__fixup_cpu' was not declared. Should it be static?
board.c:405:53: warning: Using plain integer as NULL pointer

Signed-off-by: Kim Phillips <kim.phillips@freescale.com>