firmware: raspberrypi: Introduce devm_rpi_firmware_get()

[ Upstream commit f663204c ]

It'll simplify the firmware handling for most consumers.

Suggested-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Stable-dep-of: 5bca3688 ("Input: raspberrypi-ts - fix refcount leak in rpi_ts_probe")
Signed-off-by: Sasha Levin <sashal@kernel.org>