sparc: move generic-y of exported headers to uapi/asm/Kbuild

Since commit fcc8487d477a ("uapi: export all headers under uapi
directories"), all (and only) headers under uapi directories are
exported, but asm-generic wrappers are still exceptions.

To complete de-coupling the uapi from kernel headers, move generic-y
of exported headers to uapi/asm/Kbuild.

With this change, "make headers_install" will just need to parse
uapi/asm/Kbuild to build up exported headers.

Signed-off-by: Masahiro Yamada <[e-mail]>

arch/sparc/include/asm/Kbuild

···
 generic-y += rwsem.h
 generic-y += serial.h
 generic-y += trace_clock.h
-generic-y += types.h
 generic-y += word-at-a-time.h

arch/sparc/include/uapi/asm/Kbuild

···
 # UAPI Header export list
 include include/uapi/asm-generic/Kbuild.asm
+
+generic-y += types.h