Pull out "$(SRCTREE)/" from CONFIG_SYS_FSL_PBL_PBI
and CONFIG_SYS_FSL_PBL_RCW and push it into the top Makefile.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Cc: York Sun <yorksun@freescale.com>
Cc: Poonam Aggrwal <poonam.aggrwal@freescale.com>
Cc: Valentin Longchamp <valentin.longchamp@keymile.com>