powerpc: Merge xmon

The merged version follows the ppc64 version pretty closely mostly,
and in fact ARCH=ppc64 now uses the arch/powerpc/xmon version.
The main difference for ppc64 is that the 'p' command to call
show_state (which was always pretty dodgy) has been replaced by
the ppc32 'p' command, which calls a given procedure (so in fact
the old 'p' command behaviour can be achieved with 'p $show_state').

Signed-off-by: Paul Mackerras <paulus@samba.org>
diff --git a/arch/powerpc/kernel/head_32.S b/arch/powerpc/kernel/head_32.S
index 600ea19..b102e3a 100644
--- a/arch/powerpc/kernel/head_32.S
+++ b/arch/powerpc/kernel/head_32.S
@@ -271,6 +271,9 @@
 	li	r10,MSR_KERNEL & ~(MSR_IR|MSR_DR); /* can take exceptions */ \
 	MTMSRD(r10);			/* (except for mach check in rtas) */ \
 	stw	r0,GPR0(r11);	\
+	lis	r10,0x7265;		/* put exception frame marker */ \
+	addi	r10,r10,0x6773;	\
+	stw	r10,8(r11);	\
 	SAVE_4GPRS(3, r11);	\
 	SAVE_2GPRS(7, r11)