unicore32: using generic-y format for one line asm-generic files

The patch adds one-line asm-generic files in arch/unicore32/include/asm/Kbuild
Also, remove the old implementation in arch/unicore32/Makefile
see commit from Sam Ravnborg <d8ecc5cd

>
  kbuild: asm-generic support

Signed-off-by: Guan Xuetao <gxt@mprc.pku.edu.cn>
Acked-by: Arnd Bergmann <arnd@arndb.de>