sparc64: Document the shift counts used to validate linear kernel addresses.

This way we can see exactly what they are derived from, and in particular
how they would change if we were to use a different PAGE_OFFSET value.

Signed-off-by: David S. Miller <davem@davemloft.net>
Acked-by: Bob Picco <bob.picco@oracle.com>

diff --cc arch/sparc/include/asm/page_64.h
Simple merge

diff --cc arch/sparc/kernel/ktlb.S
Simple merge

diff --cc arch/sparc/mm/init_64.h
Simple merge