[1/2] firmware: add more flexible request_firmware_async function

[kbuild test robot <lkp@intel.com>]

Hi Rafał,

I love your patch! Yet something to improve:

[auto build test ERROR on linus/master]
[also build test ERROR on v4.18-rc1 next-20180622]
[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/Sebastian-Reichel/firmware-add-more-flexible-request_firmware_async-function/20180623-025750
config: powerpc-mpc834x_mds_defconfig (attached as .config)
compiler: powerpc-linux-gnu-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=powerpc 

All errors (new ones prefixed by >>):

   drivers/net/ethernet/intel/e100.o: In function `__request_firmware_async':
>> e100.c:(.text+0x4f40): multiple definition of `__request_firmware_async'
   drivers/base/firmware_loader/fallback_table.o:fallback_table.c:(.text+0x0): first defined here
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