In order to get rid of the global namespace for PWM devices, this commit
provides an alternative method, similar to that of the regulator or
clock frameworks, for registering a static mapping for PWM devices. This
works by providing a table with a provider/consumer map in the board
setup code.

With the new pwm_get() and pwm_put() functions available, usage of
pwm_request() and pwm_free() becomes deprecated.
Reviewed-by: NShawn Guo <shawn.guo@linaro.org>
Reviewed-by: NMark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: NThierry Reding <thierry.reding@avionic-design.de>