ARM: dts: Use ti,pbias compatible string for pbias

Use platform specific compatible strings instead of the common
"ti,pbias-omap" compatible string.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>