mmc: Use lldiv() for 64-bit division in write_raw_image()

This fixes compilation problems when using a hardfloat toolchain on
ARM, which manifest themselves as "libgcc.a(_udivmoddi4.o) uses
VFP register arguments, u-boot does not".

These problems have been reported in the U-Boot mailing list:
    http://lists.denx.de/pipermail/u-boot/2015-October/230314.html
    http://lists.denx.de/pipermail/u-boot/2015-October/231908.html



Signed-off-by: Siarhei Siamashka <siarhei.siamashka@gmail.com>
Reviewed-by: Tom Rini <trini@konsulko.com>