m68knommu: simplify the 5407 UART setup code

Simplify the UART setup code so that it no longer loops for each UART
present. Just make it do all the work it needs in a single function.
This will make the code easier to share when we move to a single set
of platform data for ColdFire UARTs.

Signed-off-by: Greg Ungerer <gerg@uclinux.org>