mmc: winbond: don't build on M68K

The Winbond MMC driver fails to build on ARCH=m68k so prevent
that build config. Silences these build errors:

../drivers/mmc/host/wbsd.c: In function 'wbsd_request_end':
../drivers/mmc/host/wbsd.c:212:28: error: implicit declaration of function 'claim_dma_lock' [-Werror=implicit-function-declaration]
  212 |                 dmaflags = claim_dma_lock();
../drivers/mmc/host/wbsd.c:215:17: error: implicit declaration of function 'release_dma_lock'; did you mean 'release_task'? [-Werror=implicit-function-declaration]
  215 |                 release_dma_lock(dmaflags);

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Pierre Ossman <pierre@ossman.eu>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20211017175949.23838-1-rdunlap@infradead.org


Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>