MX31: mx31pdk: Remove nand_spl config.mk file

No need to have a config.mk to only store a single line.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Acked-by: Stefano Babic <sbabic@denx.de>

nand_spl/board/freescale/mx31pdk/Makefile

 CONFIG_NAND_SPL	= y
+PAD_TO	:= 2048
 
 include $(TOPDIR)/config.mk
-include $(TOPDIR)/nand_spl/board/$(BOARDDIR)/config.mk
 
 nandobj	:= $(OBJTREE)/nand_spl/
 

nand_spl/board/freescale/mx31pdk/config.mk

-PAD_TO	:= 2048