ir-rx51: use PWM framework instead of OMAP dmtimer

Convert driver to use PWM framework instead of calling dmtimer functions
directly for PWM timer. Remove paragraph about writing to the Free Software
Foundation's mailing address while at it.

Signed-off-by: Ivaylo Dimitrov <ivo.g.dimitrov.75@gmail.com>
Acked-by: Pali Rohár <pali.rohar@gmail.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>