powerpc/booke64: Critical and machine check exception support

Add special state saving for critical and machine check exceptions.

Most of this code could be used to handle debug exceptions taken from
kernel space, but actually doing so is outside the scope of this patch.

The various critical and machine check exceptions now point to their
real handlers, rather than hanging the kernel.

Signed-off-by: Scott Wood <scottwood@freescale.com>

diff --cc arch/powerpc/include/asm/paca.h
Simple merge

diff --cc arch/powerpc/kernel/exceptions-64e.S
Simple merge

diff --cc arch/powerpc/mm/tlb_nohash.c
Simple merge