ARM: OMAP4: hwmod_data: add opt clks for dss_hdmi and dss_venc

These extra optional clocks are required as main clock for these modules
are going to be routed to the main module clock. Otherwise, the hdmi / tv
clocks are not going to be enabled during usage, leading to failure.

Signed-off-by: Tero Kristo <t-kristo@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>