m68k/lib: fix serial driver relocation

Fix coldfire serial driver bindings no more relocated to ram after last
changes to drivers/serial/serial.c (regression).
Serial initialization in ram has to be called after that gd->reloc_off is
calculated.

Signed-off-by: Angelo Dureghello <sysamfw@gmail.com>
Cc: Jason Jin <jason.jin@freescale.com>
Acked-by: Jens Scharsig (BuS Elektronik) <esw@bus-elektronik.de>
Tested-by: Jens Scharsig (BuS Elektronik) <esw@bus-elektronik.de>