MAINTAINERS: add PolarFire SoC dt bindings

So far when I added bindings for the platform I never added them to
our MAINTAINERS entry. No time like the present to improve the coverage.

Suggested-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
Acked-by: Marc Kleine-Budde <mkl@pengutronix.de> # for can
Acked-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
CC: Mark Brown <broonie@kernel.org>
CC: Wolfram Sang <wsa@kernel.org>
CC: Thierry Reding <thierry.reding@gmail.com>
CC: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
CC: Jassi Brar <jassisinghbrar@gmail.com>
CC: Linus Walleij <linus.walleij@linaro.org>
CC: Bartosz Golaszewski <brgl@bgdev.pl>
CC: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
CC: Arnd Bergmann <arnd@arndb.de>
CC: Olof Johansson <olof@lixom.net>
CC: Michael Turquette <mturquette@baylibre.com>
CC: Stephen Boyd <sboyd@kernel.org>
Link: https://lore.kernel.org/r/20220810140243.2685416-2-conor.dooley@microchip.com

'
Signed-off-by: Arnd Bergmann <arnd@arndb.de>