ARM: 9084/1: simplify the build rule of mach-types.h

The directory of mach-types.h is created a couple of lines above:

  _dummy := $(shell [ -d '$(kapi)' ] || mkdir -p '$(kapi)') \

The 'mkdir -p' command is redundant.

scripts/Kbuild.include defines real-prereqs as a shorthand for
$(filter-out $(PHONY),$^). Let's use it to simplify the code.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>