[PATCH] ppc32/8xx: Fix r3 trashing due to 8MB TLB page instantiation

Instantiation of 8MB pages on the TLB cache for the kernel static
mapping trashes r3 register on !CONFIG_8xx_CPU6 configurations.
This ensures r3 gets saved and restored.

Signed-off-by: Marcelo Tosatti <marcelo@kvack.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>