clk: ti: am335x/am4372: Add tbclk to pwm node

Add tblck to the pwm nodes. This insures that the ehrpwm driver has access
to the time-based clk.

Do not remove similar entries for ehrpwm node. Later patches will switch
from using ehrpwm node name to pwm. But to maintain ABI compatibility we
shouldn't remove the old entries.

Signed-off-by: Franklin S Cooper Jr <fcooper@ti.com>
Acked-by: Stephen Boyd <sboyd@codeaurora.org>
Acked-by: Tero Kristo <t-kristo@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>