edb93xx: change calculation un early_udelay.h

Previous code compiled with gcc-4.2.2 makes a call to
__aeabi_uidiv to divide by 20. As a side effect it was
not inline any more, and so sdram_cfg used the stack
as well, but this is early code that has no stack yet.
The patch explicitly removes the division, so no stack is used.

The calculation of the counter calls a division by 20

Signed-off-by: Alessandro Rubini <rubini@gnudd.com>