net: dsa: microchip: ksz8xxx: Replace kernel.h with the necessary inclusions

When kernel.h is used in the headers it adds a lot into dependency hell,
especially when there are circular dependencies are involved.

Replace kernel.h inclusion with the list of what is really being used.
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/41d99ef8629e1db03d4f2662f5556611e0b94652.1654323308.git.christophe.jaillet@wanadoo.frSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/dsa/microchip/ksz8.h

@@ -7,7 +7,8 @@
 
 #ifndef __KSZ8XXX_H
 #define __KSZ8XXX_H
-#include <linux/kernel.h>
+
+#include <linux/types.h>
 
 enum ksz_regs {
 	REG_IND_CTRL_0,