powerpc/boot: Expose Kconfig symbols to wrapper

Currently the wrapper is built without including anything in
$(src)/include/, which means there are no CONFIG_ symbols defined.
This means the platform specific serial drivers were never enabled.

We now copy the definitions into the boot directory, so any C file can
now include autoconf.h to depend on configuration options.

Fixes: 866bfc75f40e ("powerpc: conditionally compile platform-specific serial drivers")
Signed-off-by: Joel Stanley <[e-mail]>
[mpe: Fix to use $(objtree) to find autoconf.h]
Signed-off-by: Michael Ellerman <[e-mail]>

arch/powerpc/boot/.gitignore

···
 fdt_wip.c
 libfdt.h
 libfdt_internal.h
+autoconf.h
 

arch/powerpc/boot/Makefile

···
 $(obj)/zImage.coff.lds $(obj)/zImage.ps3.lds : $(obj)/%: $(srctree)/$(src)/%.S
 	$(Q)cp $< $@
 
+$(obj)/serial.c: $(obj)/autoconf.h
+
+$(obj)/autoconf.h: $(obj)/%: $(objtree)/include/generated/%
+	$(Q)cp $< $@
+
 clean-files := $(zlib-) $(zlibheader-) $(zliblinuxheader-) \
 		$(zlib-decomp-) $(libfdt) $(libfdtheader) \
-		empty.c zImage.coff.lds zImage.ps3.lds zImage.lds
+		autoconf.h empty.c zImage.coff.lds zImage.ps3.lds zImage.lds
 
 quiet_cmd_bootcc = BOOTCC  $@
       cmd_bootcc = $(BOOTCC) -Wp,-MD,$(depfile) $(BOOTCFLAGS) -c -o $@ $<

arch/powerpc/boot/serial.c

···
 #include "stdio.h"
 #include "io.h"
 #include "ops.h"
+#include "autoconf.h"
 
 static int serial_open(void)
 {