ARM: hide mach-*/ include for ARM_SINGLE_ARMV7M

The machine specific header files are exported for traditional
platforms, but not for the ones that use ARCH_MULTIPLATFORM, as
they could conflict with one another.

In case of ARM_SINGLE_ARMV7M, we end up also exporting them,
but that appears to be a mistake, and we should treat it the
same way as ARCH_MULTIPLATFORM here.

'make W=1' warns about this because it passes -Wmissing-includes
to gcc and the directories are not actually present.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

arch/arm/Makefile

@@ -260,12 +260,14 @@ machdirs := $(patsubst %,arch/arm/mach-%/,$(machine-y))
 platdirs := $(patsubst %,arch/arm/plat-%/,$(sort $(plat-y)))
 
 ifneq ($(CONFIG_ARCH_MULTIPLATFORM),y)
+ifneq ($(CONFIG_ARM_SINGLE_ARMV7M),y)
 ifeq ($(KBUILD_SRC),)
 KBUILD_CPPFLAGS += $(patsubst %,-I%include,$(machdirs) $(platdirs))
 else
 KBUILD_CPPFLAGS += $(patsubst %,-I$(srctree)/%include,$(machdirs) $(platdirs))
 endif
 endif
+endif
 
 export	TEXT_OFFSET GZFLAGS MMUEXT