After check the code, 'bswapsi2' and 'muldi3' are useless for
unicore32, so can remove them to avoid compiling failure.

The related error (with allmodconfig under unicore32):

    LD      init/built-in.o
  arch/unicore32/kernel/built-in.o:(___ksymtab+__muldi3+0x0): undefined reference to `__muldi3'
  arch/unicore32/kernel/built-in.o:(___ksymtab+__bswapsi2+0x0): undefined reference to `__bswapsi2'
Signed-off-by: NChen Gang <gang.chen.5i5j@gmail.com>
Acked-by: NXuetao Guan <gxt@mprc.pku.edu.cn>
Signed-off-by: NXuetao Guan <gxt@mprc.pku.edu.cn>