ARM: OMAP2+: DRA7: realtime_counter: Add ratio registers for 20MHZ sys-clk frequency

ARM: OMAP2+: DRA7: realtime_counter: Add ratio registers for 20MHZ sys-clk frequency

The real time counter also called master counter, is a free-running
counter. It produces the count used by the CPU local timer peripherals
in the MPU cluster. The timer counts at a rate of 6.144 MHz.

The ratio registers are missing for a sys-clk of 20MHZ which is used
by DRA7 socs. So because of this, the counter was getting wrongly
programmed for a sys-clk of 38.4Mhz(default). So adding the ratio
registers for 20MHZ sys-clk.

Tested-by: Nishanth Menon <nm@ti.com>
Acked-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Signed-off-by: Sricharan R <r.sricharan@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>