powerpc: change CONFIG_6xx to CONFIG_PPC_BOOK3S_32

Today we have:

config PPC_BOOK3S_32
	bool "512x/52xx/6xx/7xx/74xx/82xx/83xx/86xx"
	[depends on PPC32 within a choice]

config PPC_BOOK3S
	def_bool y
	depends on PPC_BOOK3S_32 || PPC_BOOK3S_64

config 6xx
	def_bool y
	depends on PPC32 && PPC_BOOK3S

6xx is therefore redundant with PPC_BOOK3S_32.

In order to make the code clearer, lets use preferably PPC_BOOK3S_32.
This will allow to remove CONFIG_6xx in a later patch.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
diff --git a/arch/powerpc/include/asm/reg.h b/arch/powerpc/include/asm/reg.h
index de52c31..0d2139a 100644
--- a/arch/powerpc/include/asm/reg.h
+++ b/arch/powerpc/include/asm/reg.h
@@ -582,7 +582,7 @@
 #define HID0_POWER9_RADIX	__MASK(63 - 8)
 
 #define SPRN_HID1	0x3F1		/* Hardware Implementation Register 1 */
-#ifdef CONFIG_6xx
+#ifdef CONFIG_PPC_BOOK3S_32
 #define HID1_EMCP	(1<<31)		/* 7450 Machine Check Pin Enable */
 #define HID1_DFS	(1<<22)		/* 7447A Dynamic Frequency Scaling */
 #define HID1_PC0	(1<<16)		/* 7450 PLL_CFG[0] */