power/reset: at91-reset: allow compiling as a module

It was not possible to compile at91-reset as a module. Implement .remove()
to allow it. Also switch to module_platform_driver_probe() as it is not
hotpluggable.

Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Signed-off-by: Sebastian Reichel <sre@kernel.org>

drivers/power/reset/Kconfig

@@ -23,7 +23,7 @@ config POWER_RESET_AT91_POWEROFF
 	  SoCs
 
 config POWER_RESET_AT91_RESET
-	bool "Atmel AT91 reset driver"
+	tristate "Atmel AT91 reset driver"
 	depends on ARCH_AT91
 	default SOC_AT91SAM9 || SOC_SAMA5
 	help