ARM: dts: dra7: Correct clock tree for sys_32k_ck

ARM: dts: dra7: Correct clock tree for sys_32k_ck

This is w.r.t J6/J6eco: 32clk is pseudo (erratum i856) - clock source.
Errata i856 for the AM572x (DRA7xx) points out that the 32.768KHz external
crystal is not enabled at power up. Instead the CPU falls back to using
an emulation for the 32KHz clock which is SYSCLK1/610.  SYSCLK1 is usually
20MHz on boards so far (which gives an emulated frequency of 32.786KHz)

Modelling the same in device tree.

Acked-by: Tero Kristo <t-kristo@ti.com>
Signed-off-by: Keerthy <j-keerthy@ti.com>
Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>