feat(runtime): for each CPU only map their own stack respectively

This commit changes the memory mapping of the stack area. Instead of
flat-mapping the whole stack area for each CPU, only map the stack
area for that particular CPU in the High region.

For this to work, the following changes are made:
 - move the mapping of the high region out from the realm lib to the
   xlat library
 - move the build time config option RMM_NUM_PAGES_PER_STACK to the xlat
   library.
 - add a new mm region to the high VA space for the stack of that CPU.
 - reorder segments in the linker script so that `.percpu` segment is
   the last. Change flat-mapping configurations so that the `.percpu`
   segment is not added.

Change-Id: I997c1b5ff2b972807d75692b5efc9075c5a29a30
Signed-off-by: Mate Toth-Pal <mate.toth-pal@arm.com>
17 files changed