arm64: dts: ti: Fix compatible of ti,*-ehrpwm-tbclk

TI EHRPWM compatible is just ti,*-ehrpwm-tbclk without needing a
syscon compatibility.

Fixes the following dtbs_check warnings:
 compatible: [''ti,am654-ehrpwm-tbclk, 'syscon'] is too long
 compatible: ['ti,am64-epwm-tbclk', 'syscon'] is too long
 compatible: ['ti,am62-epwm-tbclk', 'syscon'] is too long

Reviewed-by: Vignesh Raghavendra <vigneshr@ti.com>
Link: https://lore.kernel.org/r/20230713184759.3336536-1-nm@ti.com


Signed-off-by: Nishanth Menon <nm@ti.com>