BACKPORT: FROMLIST: pwm: Add support for different PWM output types

Normally, PWM channels have fixed output until software requests to
change their settings. There are some PWM devices whose outputs can be
changed autonomously according to a predefined pattern programmed in
hardware.

Add support for such devices by adding a new pwm_output_type enum type
to identify these two different PWM types and adding helper functions to
read the PWM output type supported by a PWM.

Bug: 140290585
Link: https://lore.kernel.org/lkml/1568415464-20267-1-git-send-email-gurus@codeaurora.org/


Change-Id: Ie8d61975057c51258e5bde9451ce96be4acdf98b
Signed-off-by: Fenglin Wu <fenglinw@codeaurora.org>
[gurus@codeaurora.org: removed output_pattern, changed output_type sysfs
param to read-only, reworded commit message]
Signed-off-by: Guru Das Srinagesh <gurus@codeaurora.org>