powerpc, mpc83xx: add missing functions to include/common.h

add following functions to common.h, to prevent
extern declarations:

void disable_addr_trans(void);
void enable_addr_trans(void);
void ddr_enable_ecc(unsigned int dram_size);

Signed-off-by: Heiko Schocher <hs@denx.de>
Acked-by: Kim Phillips <kim.phillips@freescale.com>
cc: Kim Phillips <kim.phillips@freescale.com>
cc: Holger Brunck <holger.brunck@keymile.com>
cc: Wolfgang Denk <wd@denx.de>
cc: Detlev Zundel <dzu@denx.de>
cc: Valentin Longchamp <valentin.longchamp@keymile.com>