[PATCH] video: fbdev: gbefb: add COMPILE_TEST support

[kbuild test robot]

Hi Bartlomiej,

I love your patch! Yet something to improve:

[auto build test ERROR on linus/master]
[also build test ERROR on v5.1-rc4 next-20190412]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url:    https://github.com/0day-ci/linux/commits/Bartlomiej-Zolnierkiewicz/video-fbdev-gbefb-add-COMPILE_TEST-support/20190413-072821
config: arm-allyesconfig (attached as .config)
compiler: arm-linux-gnueabi-gcc (Debian 7.2.0-11) 7.2.0
reproduce:
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # save the attached .config to linux build tree
        GCC_VERSION=7.2.0 make.cross ARCH=arm 

All errors (new ones prefixed by >>):

   drivers/video/fbdev/gbefb.o: In function `gbe_turn_off':
>> gbefb.c:(.text+0x9b8): undefined reference to `__bad_udelay'
   gbefb.c:(.text+0xa0c): undefined reference to `__bad_udelay'
   drivers/video/fbdev/gbefb.o: In function `gbe_turn_on':
   gbefb.c:(.text+0xb64): undefined reference to `__bad_udelay'
   gbefb.c:(.text+0xbb0): undefined reference to `__bad_udelay'
   drivers/video/fbdev/gbefb.o: In function `gbefb_set_par':
   gbefb.c:(.text+0xda4): undefined reference to `__bad_udelay'

---
0-DAY kernel test infrastructure                Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all                   Intel Corporation
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