ARM: dts: AM437X-SK-EVM: Remove redundant regulator compatibles

With the device tree parsing using the regulator framework
there is a no longer a need for separate compatibles for
individual regulator nodes. Hence removing them all.

Signed-off-by: Keerthy <j-keerthy@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>