We now have memory organised in a way that allows
implementing KASAN.

Unlike book3s/64, book3e always has translation active so the only
thing needed to use KASAN is to setup an early zero shadow mapping
just after setting a stack pointer and before calling early_setup().

The memory layout is now as follows

   +------------------------+  Kernel virtual map end (0xc000200000000000)
   |                        |
   |    16TB of KASAN map   |
   |                        |
   +------------------------+  Kernel KASAN shadow map start
   |                        |
   |    16TB of IO map      |
   |                        |
   +------------------------+  Kernel IO map start
   |                        |
   |    16TB of vmemmap     |
   |                        |
   +------------------------+  Kernel vmemmap start
   |                        |
   |    16TB of vmap        |
   |                        |
   +------------------------+  Kernel virt start (0xc000100000000000)
   |                        |
   |    64TB of linear mem  |
   |                        |
   +------------------------+  Kernel linear (0xc.....)
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/0bef8beda27baf71e3b9e8b13e620fba6e19499b.1656427701.git.christophe.leroy@csgroup.eu