rk2928:

rk2928:
eliminate the build error using rk2928_tb_defconfig/rk2928_sdk_defconfig.
as the following:
  UPD     include/generated/compile.h
  CC      init/version.o
  LD      init/built-in.o
  LD      .tmp_vmlinux1
drivers/built-in.o: In function rk29_sdmmc_gpio_open'
make: *** [.tmp_vmlinux1] Error 1