kernel/configs: use .incbin directive to embed config_data.gz

This slightly optimizes the kernel/configs.c build.

bin2c is not very efficient because it converts a data file into a huge
array to embed it into a *.c file.

Instead, we can use the .incbin directive.

Also, this simplifies the code; Makefile is cleaner, and the way to get
the offset/size of the config_data.gz is more straightforward.

I used the "asm" statement in *.c instead of splitting it into *.S
because MODULE_* tags are not supported in *.S files.

I also cleaned up kernel/.gitignore; "config_data.gz" is unneeded
because the top-level .gitignore takes care of the "*.gz" pattern.

[yamada.masahiro@socionext.com: v2]
  Link: http://lkml.kernel.org/r/1550108893-21226-1-git-send-email-yamada.masahiro@socionext.com
Link: http://lkml.kernel.org/r/1549941160-8084-1-git-send-email-yamada.masahiro@socionext.com
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Alexander Popov <alex.popov@linux.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Richard Guy Briggs <rgb@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/Makefile

@@ -116,17 +116,8 @@ obj-$(CONFIG_GCC_PLUGIN_STACKLEAK) += stackleak.o
 KASAN_SANITIZE_stackleak.o := n
 KCOV_INSTRUMENT_stackleak.o := n
 
-$(obj)/configs.o: $(obj)/config_data.h
+$(obj)/configs.o: $(obj)/config_data.gz
 
 targets += config_data.gz
 $(obj)/config_data.gz: $(KCONFIG_CONFIG) FORCE
 	$(call if_changed,gzip)
-
-filechk_ikconfiggz = \
-	echo "static const char kernel_config_data[] __used = MAGIC_START"; \
-	cat $< | scripts/bin2c; \
-	echo "MAGIC_END;"
-
-targets += config_data.h
-$(obj)/config_data.h: $(obj)/config_data.gz FORCE
-	$(call filechk,ikconfiggz)