MIPS: Only include the platform file needed

Instead of including all Platform files, we simply include the
needed one and avoid clashes with makefile variables.

Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

arch/mips/ath25/Platform

@@ -1,6 +1,5 @@
 #
 # Atheros AR531X/AR231X WiSoC
 #
-platform-$(CONFIG_ATH25)	+= ath25/
 cflags-$(CONFIG_ATH25)		+= -I$(srctree)/arch/mips/include/asm/mach-ath25
 load-$(CONFIG_ATH25)		+= 0xffffffff80041000