drm/omap: support type B PLL for DPI

Type A and B PLLs require a bit different calculations for the clock
rates. DPI driver supports only type A PLLs.

This patch adds support for the type B PLL.

Type B PLLs are simpler than type A, as type B can produce a good clock
for almost any rate. Thus we can just ask it to produce the pixel clock
and use one as LCK and PCK dividers.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>