clk: sifive: Allow building the driver as a module

This can reduce the kernel image size in multiplatform configurations.

Signed-off-by: Samuel Holland <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Stephen Boyd <[e-mail]>

drivers/clk/sifive/Kconfig

···
 if CLK_SIFIVE
 
 config CLK_SIFIVE_PRCI
-	bool "PRCI driver for SiFive SoCs"
+	tristate "PRCI driver for SiFive SoCs"
 	default ARCH_SIFIVE
 	select RESET_CONTROLLER
 	select RESET_SIMPLE

drivers/clk/sifive/sifive-prci.c

···
 #include <linux/clkdev.h>
 #include <linux/delay.h>
 #include <linux/io.h>
+#include <linux/module.h>
 #include <linux/of.h>
 #include "sifive-prci.h"
 #include "fu540-prci.h"
···
 	},
 	.probe = sifive_prci_probe,
 };
+module_platform_driver(sifive_prci_driver);
 
-static int __init sifive_prci_init(void)
-{
-	return platform_driver_register(&sifive_prci_driver);
-}
-core_initcall(sifive_prci_init);
+MODULE_AUTHOR("Paul Walmsley <[e-mail]>");
+MODULE_DESCRIPTION("SiFive Power Reset Clock Interface (PRCI) driver");
+MODULE_LICENSE("GPL");