kbuild: replace genhdr-y with generated-y

Originally, generated-y and genhdr-y had different meaning, like
follows:

- generated-y: generated headers (other than asm-generic wrappers)
- header-y   : headers to be exported
- genhdr-y   : generated headers to be exported (generated-y + header-y)

Since commit fcc8487d477a ("uapi: export all headers under uapi
directories"), headers under UAPI directories are all exported.
So, there is no more difference between generated-y and genhdr-y.

We see two users of genhdr-y, arch/{arm,x86}/include/uapi/asm/Kbuild.
They generate some headers in arch/{arm,x86}/include/generated/uapi/asm
directories, which are obviously exported.

Replace them with generated-y, and abolish genhdr-y.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
diff --git a/scripts/Makefile.asm-generic b/scripts/Makefile.asm-generic
index e4d017d5..95f7d80 100644
--- a/scripts/Makefile.asm-generic
+++ b/scripts/Makefile.asm-generic
@@ -15,7 +15,7 @@
 
 # Stale wrappers when the corresponding files are removed from generic-y
 # need removing.
-generated-y   := $(generic-y) $(genhdr-y) $(generated-y)
+generated-y   := $(generic-y) $(generated-y)
 all-files     := $(patsubst %, $(obj)/%, $(generated-y))
 old-headers   := $(wildcard $(obj)/*.h)
 unwanted      := $(filter-out $(all-files),$(old-headers))