clk: ti816x: Add missing dmtimer clkdev entries

Add missing clkdev dmtimer related entries for dm816x.
32Khz and ext sources were missing.

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Cc: Brian Hutchinson <b.hutchman@gmail.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Tero Kristo <t-kristo@ti.com>