staging: sm750fb: move MHz() and roundedDiv() close to their usage

The MHz() and roundedDiv macros are used only by ddk750_chip.c, so move
their definition there.

Signed-off-by: Mike Rapoport <mike.rapoport@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>