85xx: Round up frequency calculations to get reasonable output

eg. because of rounding error we can get 799Mhz instead of 800Mhz.

Introduced DIV_ROUND_UP and roundup taken from linux kernel.

Signed-off-by: Dejan Minic <minic@freescale.com>
Signed-off-by: Srikanth Srinivasan <srikanth.srinivasan@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>
Acked-by: Andy Fleming <afleming@freescale.com>