Fixed misspelled 'disable' in help text.

Signed-off-by: Sébastien Szymanski <sebastien.szymanski@armadeus.com>

The first name is taken from command name that's why shouldn't be listed in
help. And commands shouldn't be listed with <> which means value but value
itself is command name.
Also add description for commands to make it clear what it does.

Before
pwm pwm <invert> <pwm_dev_num> <channel> <polarity>
pwm <config> <pwm_dev_num> <channel> <period_ns> <duty_ns>
...

After:
pwm invert <pwm_dev_num> <channel> <polarity> - invert polarity
pwm config <pwm_dev_num> <channel> <period_ns> <duty_ns> - config PWM
pwm enable <pwm_dev_num> <channel> - enable PWM output
pwm disable <pwm_dev_num> <channel> - disable PWM output

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

It is a pain to have to specify the value 10 in each call. Add a new
dectoul() function and update the code to use it.

Signed-off-by: Simon Glass <sjg@chromium.org>

Currently, we check argc in a number of places to make sure that we have
all of the required arguments for each of the pwm sub-commands.
However, there's at least one place where we've got dead code as we'll
never have argc == 0, due to checking that argc was at least 4 earlier
and having only subtracted 3.  Rework things so that when we have
determined our subcommand make sure we have the right number of
arguments for it, or error out.  This means we can stop checking against
argc again later.

Reported-by: Coverity (CID: 316601)
Cc: Pragnesh Patel <pragnesh.patel@sifive.com>
Signed-off-by: Tom Rini <trini@konsulko.com>

Add the command "pwm" for controlling the pwm channels. This
command provides pwm invert/config/enable/disable functionalities
via PWM uclass drivers

Signed-off-by: Pragnesh Patel <pragnesh.patel@sifive.com>
Reviewed-by: Simon Glass <sjg@chromium.org>