powerpc: Switch back to struct platform_driver::remove()

After commit 0edb555a ("platform: Make platform_driver::remove()
return void") .remove() is (again) the right callback to implement for
platform drivers.

Convert all pwm drivers to use .remove(), with the eventual goal to drop
struct platform_driver::remove_new(). As .remove() and .remove_new() have
the same prototypes, conversion is done by just changing the structure
member name in the driver initializer.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@baylibre.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20240909130902.851274-2-u.kleine-koenig@baylibre.com