MIPS: Introduce support for Platform definitions

Move platform specific definitions to the platfrom directories.

Each platform shall do the following:
1) include an entry in arch/mips/Kbuild.platforms
2) add relevant definitions to arch/mips/<platform>/Platform

This commits changes ar7 to the new scheme as an example.

Introducing a platform speecific Platfrom file has following advantages:
1) decentralization of platfrom definitions
2) simplification af arch/mips/Makefile
3) force all platfrom to build with -Werror (done in arch/mips/Kbuild)

[Ralf: Remove forgotten -Werror from AR7 Makefile]

Signed-off-by: Sam Ravnborg <[e-mail]>
To: linux-mips <[e-mail]>
To: Wu Zhangjin <[e-mail]>
Patchwork: https://patchwork.linux-mips.org/patch/1302/
Patchwork: http://patchwork.linux-mips.org/patch/1308/
Signed-off-by: Ralf Baechle <[e-mail]>

arch/mips/Kbuild

···
 # CFLAGS_<file.o> := -Wno-error
 subdir-ccflags-y := -Werror
 
+# platform specific definitions
+include arch/mips/Kbuild.platforms
+obj-y := $(platform-y)
 
 # mips object files
 # The object files are linked as core-y files would be linked

arch/mips/Kbuild.platforms

···
+# All platforms listed in alphabetic order
+
+platforms += ar7
+
+# include the platform specific files
+include $(patsubst %, $(srctree)/arch/mips/%/Platform, $(platforms))

arch/mips/Makefile

···
 #
 # Board-dependent options and extra files
 #
-
-#
-# Texas Instruments AR7
-#
-core-$(CONFIG_AR7)		+= arch/mips/ar7/
-cflags-$(CONFIG_AR7)		+= -I$(srctree)/arch/mips/include/asm/mach-ar7
-load-$(CONFIG_AR7)		+= 0xffffffff94100000
+include $(srctree)/arch/mips/Kbuild.platforms
 
 #
 # Acer PICA 61, Mips Magnum 4000 and Olivetti M700.

arch/mips/ar7/Makefile

···
 	platform.o \
 	gpio.o \
 	clock.o
-EXTRA_CFLAGS += -Werror

arch/mips/ar7/Platform

···
+#
+# Texas Instruments AR7
+#
+platform-$(CONFIG_AR7)          += ar7/
+cflags-$(CONFIG_AR7)            += -I$(srctree)/arch/mips/include/asm/mach-ar7
+load-$(CONFIG_AR7)              += 0xffffffff94100000