ARM: dts: am43x-epos-evm: Add VPFE and OV2659 entries

Add VPFE device nodes entries.
Add OmniVision OV2659 sensor device nodes and linkage.

Since Rev1.2a on this board the sensor source clock (xvclk) has a
dedicated 12Mhz oscillator instead of using clkout1.
Add 'audio_mstrclk' fixed clock object to represent it.

Signed-off-by: Benoit Parrot <bparrot@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>