ARM: AM33XX: clk: Add clock node for EHRPWM TBCLK

EHRPWM module requires explicit clock gating of TBCLK from control
module. Hence add TBCLK clock node in clock tree for EHRPWM modules.

Signed-off-by: Philip Avinash <avinashphilip@ti.com>
[bigeasy: remove CK_AM33XX]
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Paul Walmsley <paul@pwsan.com>