arm64: dts: ti: k3-am62-main: Add epwm nodes

Add the compatible DT nodes for all EPWM instances
present in AM62 SoC. There is a total of 3 EPWM modules
available, sharing the same K3 IP as in AM64 SoC.

This also adds a required "ti,am62-epwm-tbclk" clock
provider node for the EPWM time-base clock.

Signed-off-by: Georgi Vlaev <g-vlaev@ti.com>
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>
Link: https://lore.kernel.org/r/20220531205229.198011-2-g-vlaev@ti.com