kernel: b53: drop support for old location of bcm47xx_nvram.h

In kernels 4.0 and older that header file was located in some subdir of
arch/mips/include. Target brcm47xx supports kernels 4.4 and 4.9 only so
that code isn't needed anymore.

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>

target/linux/generic/files/drivers/net/phy/b53/b53_priv.h

@@ -310,14 +310,12 @@ static inline int b53_write64(struct b53_device *dev, u8 page, u8 reg,
 }
 
 #ifdef CONFIG_BCM47XX
+#include <bcm47xx_board.h>
 
 #include <linux/version.h>
 #if (LINUX_VERSION_CODE >= KERNEL_VERSION(4, 1, 0))
 #include <linux/bcm47xx_nvram.h>
-#else
-#include <bcm47xx_nvram.h>
 #endif
-#include <bcm47xx_board.h>
 static inline int b53_switch_get_reset_gpio(struct b53_device *dev)
 {
 	enum bcm47xx_board board = bcm47xx_board_get();