pwm: tegra: Add support for Tegra186

Tegra186 has multiple PWM controllers with only one output instead of
one controller with four outputs in earlier SoC generations.

Add support for Tegra186 and detect the number of PWM outputs using
device tree match data.

Signed-off-by: Laxman Dewangan <ldewangan@nvidia.com>
Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>