mpc83xx: Introduce ARCH_MPC837X

Replace CONFIG_MPC837x with a proper CONFIG_ARCH_MPC837X Kconfig option.

Signed-off-by: Mario Six <mario.six@gdsys.cc>
diff --git a/arch/powerpc/include/asm/mpc8xxx_spi.h b/arch/powerpc/include/asm/mpc8xxx_spi.h
index 0c2bdb3..b583a32 100644
--- a/arch/powerpc/include/asm/mpc8xxx_spi.h
+++ b/arch/powerpc/include/asm/mpc8xxx_spi.h
@@ -14,7 +14,7 @@
 	defined(CONFIG_ARCH_MPC8313) || \
 	defined(CONFIG_ARCH_MPC8315) || \
 	defined(CONFIG_ARCH_MPC834X) || \
-	defined(CONFIG_MPC837x)
+	defined(CONFIG_ARCH_MPC837X)
 
 typedef struct spi8xxx {
 	u8 res0[0x20];	/* 0x0-0x01f reserved */