pwm: tiehrpwm: Don't use emulation mode bits to control PWM output

As per AM335x TRM SPRUH73P "15.2.2.11 ePWM Behavior During Emulation",
TBCTL[15:14] only have effect during emulation suspend events (IOW,
to stop PWM when debugging using a debugger). These bits have no effect
on PWM output during normal running of system. Hence, remove code
accessing these bits as they have no role in enabling/disabling PWMs.

Fixes: 19891b20

 ("pwm: pwm-tiehrpwm: PWM driver support for EHRPWM")
Cc: stable@vger.kernel.org
Signed-off-by: Vignesh R <vigneshr@ti.com>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>