Monahans: avoid floating point calculations

Current code for the Monahans CPU defined OSCR_CLK_FREQ as 3.250 (MHz)
which caused floating point operations to be used. This resulted in
unresolved references to some FP related libgcc functions when using
U-Boot's private libgcc functions.

Change the code to use fixed point math only.

Signed-off-by: Wolfgang Denk <wd@denx.de>